Mizuiro went to Hiragi Junior High, along with Keigo. He met Ichigo and Chad on the first day of High School. Mizuiro went up and introduced himself to Ichigo and Chad despite Keigo telling him "Kurosaki and Sado" were rumored to be "hoodlum bullies from hell". Mizuiro reasons that if it is only a rumor then it might not be true, because Mizuiro introduced himself to Chad and Ichigo, the hoodlums who were fighting with Ichigo turned on Keigo and Mizuiro. As Keigo was being stumped on the back, Mizuiro explained who Keigo was, greatly praising him to Ichigo. Ichigo noted how unusual it was for a guy to praise his friends like that and asked Mizuiro if he was good at making excuses. Mizuiro answered in the affirmative and so Ichigo asked him to make a good excuse so that he and Chad were not suspended for saving Keigo. As Ichigo rushes off to save Keigo, Mizuiro notes that he is filled with a feeling of happiness, noting that communication has been established.
When Mizuiro first met Rukia Kuchiki, Ichigo warned her that he was sly with the ladies. When Mizuiro countered by saying he prefers older women, Ichigo comments that's why he warned Rukia to be careful. Which leaves Mizuiro confused. Mizuiro is resourceful, level-headed, and calm even in detrimental circumstances. He can maintain his cool even in the presence of Aizen. These traits allow him to think straight, and plan contingencies ahead of time. He also likes to tease his classmate and friend by calling him "Asano-san" (Mr. Asano in the English version). When he is overreacting, which makes him even more agitated. Despite his cheerful appearance he can be quite cruel, shown by not accepting his own mother. Keigo mentions that Mizuiro is good at "putting up walls", and the only person he ever really opened up to is Ichigo.
Mizuiro has short black hair and green eyes, parted down the middle with a stray bang in his face and the tips fanning out. He looks very young and wears the Karakura uniform with the jacket zipped up. 17 months later, his hair is now straight and has grown out to cover his ears.
Mizuiro is able to maintain his existence in the presence of the Hōgyoku transformed Aizen.
Mizuiro has shown to have an aptitude for coming up with improvised weaponry, and comes up with ideas to attack Aizen, such as making bombs to attack him with and bringing stun guns for use by himself and others, in order to "fight" against Aizen.
Agents of Shinigami arc
Mizuiro is first seen in Karakura High School, explaining to Tatsuki and Orihime that Ichigo might not come to school because a truck crashed into his house the night before. He assures them that no one was hurt, but Ichigo was needed to help clean-up the mess. When Ichigo shows up at school later that day, Mizuiro reminds Ichigo that they have social studies for 3rd period. They are interrupted by Rukia, who Mizuiro introduces as a new transfer student. Ichigo is shocked at Mizuiro's declaration, but Rukia prevents him from causing a scene.
After Ichigo agrees to assist Rukia with her Shinigami duties, Mizuiro is seen joining them for lunch and warns Ichigo about how it appears to others that he hangs around Rukia so much. Ichigo responds that if he cared about what others thought he would have dyed his hair black a long time ago. As Mizuiro starts to introduce himself to Rukia, Ichigo interjects that Mizuiro's hobby is womanizing. Mizuiro is mortified at Ichigo's accusation, but Ichigo presses ahead and warns Rukia to be careful. Mizuiro protests that he only dates older women. Ichigo responds that that is why he is warning Rukia. They are then joined by Keigo, who wonders what Rukia is doing there. Mizuiro pipes in that Ichigo lured Rukia up there. Ichigo tries to protest, but is ignored. He is present with Chad when he introduces his newly acquired talking parakeet. The following day, Ichigo rushes in to their classroom and collars Mizuiro, demanding to know where Chad is. Mizuiro tells Ichigo that he has not seen Chad, Ichigo immediately rushes away.
Mizuiro is next seen with the rest of Ichigo's friends, wondering why Chad's Parakeet is no longer talking. He then greets Rukia and notes that the other is unusually late to school. Shortly after, Mizuiro appears with Keigo and Chad, wondering where Ichigo has gone to. He is harassed by Keigo for being popular with the girls, when he attempts to teach Keigo about liking both Rukia and Orihime, or any girl who is pretty. Mizuiro then seeks sanctuary with Chad just as they arrive at their classroom and find Tatsuki in a fell mood. Mizuiro is rightly terrified. They are then interrupted by a teacher, who demands to know what's going on. The other girls start to blame Ichigo, but Orihime interjects and informs the others that, the person who caused the commotion was not Ichigo. Mizuiro, along with Keigo, then wonders what is going on.
The next day, the 16th of June, Mizuiro arrives at Ichigo's house to walk with him to school per normal. As Ichigo is running late, he invites Mizuiro inside as he gets ready, which is when Ichigo notices that Mizuiro has had his memory altered to erase the events of the day before. He is then seen hanging out with Ichigo, and Keigo at school.
Mizuiro is next seen doing Don Kanonji's trademark "Bohahahaha" greeting to Ichigo. The Wednesday after that day, Mizuiro is seen with the others as the Don Kanoji's filming site, the old Karakura Hospital. Mizuiro joins Keigo in confronting Ichigo with the fact that he turned-up to the shoot despite previously saying he would not. When Orihime comes to apologies to Ichigo for doing the Bohahahaha greeting when he despises the show, Ichigo revels that Mizuiro, as well as Keigo, knowingly harass Ichigo with the Bohahahaha greeting. As the night progress, Mizuiro tells Keigo to stop with the Bohahahaha greeting as the pose has no meaning without the guy who hates it (Ichigo). Keigo tries to get Mizuiro to do the pose just with him just as Mizuiro spot a pair of pretty ladies. Mizuiro plays cute, and pretends not to know the pose, the ladies immediately groom on to him as Keigo is left crying on the ground. Mizuiro witnesses Ichigo rushing towards Don Kanonji when the latter unknowingly accelerates the Hollow transformation of a Demi-Hollow.
The next day, Mizuiro is called in with the others to the principal’s office to explain the disturbance they caused on Don Kanonji's show. Mizuiro escapes out the window with the others as Rukia distracts the teachers with her tears. He is later seen with the rest of the group, thanking Rukia for getting them out.
A few days later, Mizuiro is seen commenting on the poor nature of Keigo's school exam, and admitting that he is no better. When Ichigo tries to comfort Keigo, Keigo grooms on to him, and asks him to share in the pain of being morons. Mizuiro warns him not to say those things until the exam results come out and brings out the list of the top fifty students in their year based on their mid-semester marks, revealing that Ichigo was 18th in their year after the mid-semesters. As Keigo teases Ichigo for being a nerd, Mizuiro quietly compliments his academic prowess. Ichigo states that he studies hard, and keeps his marks-up so that the faculty won't be on his back due to his quick temper. Mizuiro comments on how much trouble that would be, even for Ichigo. But Ichigo brushes it aside, saying he's used to it. Mizuiro then asks why Ichigo is not hanging out with Rukia. Ichigo owns it is because there have been rumors circulating about the nature of their relationship. Unbeknown to Ichigo, Mizuiro started the rumors.
When the class rankings come-out, following the results of the final exam, Mizuiro and Keigo initially take comfort in the fact that none of them came in the top fifty. However, Keigo then notices that Ichigo came twenty-third and attempts to shield Mizuiro from the reality. Mizuiro, however, cannot bring himself to join Keigo in threatening to exclude Ichigo from their group. Keigo then turns to Chad for comfort, only to find that Chad came eleventh. Shocked and upset, Mizuiro runs away with Keigo.
They day after Ichigo and Ishida's encounter with the Menos, Mizuiro learns from Keigo that the latter saw Ishida was talking to himself. Overhearing the conversation, Ichigo deduces that Keigo was nearby, and comments on how dangerous that was. At lunch time, Mizuiro chastises Keigo for being noisy when Keigo complains about Ichigo inviting Ishida to join them. He is then seen eating lunch with the others. Even upon seeing Ishida, and Ichigo interact. Mizuro deduces that in reality that Ichigo, and Ishida are very much alike.
In the last day of school, Mizuiro reveals that he is going on holiday with his current girlfriend and nine of her friends, and that is why he cannot join Keigo at the beach. He is harassed by Keigo as a result. Mizuiro returns from his holiday, in Phuket. Just in time for the fireworks festival, with a tan that stings when Keigo slaps him, and accuses him of being a foreigner. He is with the group when Tatsuki and Orihime arrive, and is present when Tatsuki tells them how she went in the Judo competition. Mizuiro encourages the group to move closer to where the fireworks will actually take place. He eagerly joins Isshin Kurosaki, and his daughters as the former has booked a place close to the fireworks.
After Ichigo punches Keigo, he walks up to Mizuiro and greets him. The two of them then walk into their classroom, and greet their classmates. After noting that Ichigo, and Sado got tans. Keigo walks into the room, and asks them if they went off somewhere together. He then asks them if they had some summer camping romance, and Ichigo punches him yet again. Ichigo tells him to keep his imagination in check. He then runs off crying.
A few days later, Mizuiro and the others greet Rukia when she returns to do battle with the Bounts. A while later, Mizuiro shows Keigo that he has acquired two tickets to a show. But says he has a date, and can't make it. He hands the tickets to Keigo instead, and asks if he can get someone else to go with him. Before they can continue, Ririn detects the presence of Ryo Utagawa, and Ichigo's group leaves to confront him. Keigo whines about being left out. Which causes Mizuiro to comment that Ichigo, and the others just don't like him, much to Keigo's chagrin.
On the first day of the new semester, Mizuiro greets Ichigo and Keigo. Mizuiro refrains from comment when Keigo expresses a desire to be as open about his desires for girls such as Chizuru Honshō. Mizuiro is also present when Shinji becomes over familiar with Orihime, and hugs her in class. He teases Keigo for being hurt by Shinji's familiar nature.
After Rukia cheers up Ichigo (a bit somewhat violently) after he was defeated by Ulquiorra Cifer, and Yammy Llargo, Mizuiro is shown calling Keigo "Asano-san" which drives Keigo crazy. Then they notice Toshiro Hitsugaya's team causing chaos in their class. Unlike Keigo, Mizuiro does not interact with the Shinigami group. After they leave, comically steps on Keigo, telling him "you[Keigo] make a superb foot-rest, Asano-san", to which Keigo angrily says he will kill him.
Later that night, Mizuiro is seen talking on his cell phone with an unnamed friend. He threatens to leave Keigo behind if he doesn't stop talking. Just then, Keigo spots a weird flying creature in the sky, but this only makes Mizuiro want to leave the former behind all the more, still calling Keigo "Asano-san".
The day after Orihime Inoue is kidnapped by Ulquiorra, Mizuiro and Keigo welcome Ichigo back to school after a long absence (due to the latter's training with the Visored, and his second fight with Grimmjow Jaegerjaquez). Mizuiro once again stomps on Keigo, and offers Ichigo tickets to a winter concert. After a long pause, Ichigo agrees to go. Ichigo is then confronted by Tatsuki about his fight with the Arrancar, and asks what he has been doing. She then becomes violent when he refuses to tell her anything about it. As Tatsuki continues to scream her head off, Ichigo tells Mizuiro and Keigo to look after Tatsuki, and also to stay far away from him. Later that evening, Mizuiro and the others secretly follow Ichigo to the Urahara Shop. and witness him as well as Uryu Ishida and Yasutora "Chad" Sado's departure to Hueco Mundo.
A while later, Keigo asks Mizuiro to join the Karakura-Raizer Team, but Mizuiro rejects the offer with a cheerful expression on his face, highly implying that he doesn't believe the story about his friend witnessing the attack on Don Kanonji. Instead, Chizuru Honsho, who overheard the conversation, joined instead.
The New Captain Shunsuke Amagi arc
Mizuiro is seen at school as Ichigo, Chad, and Tatsuki arrive for classes. He comments that Keigo looks like a rug when the latter ends-up on the floor due to his antics. When Rurichiyo Kasumioji attends class for the first time, Mizuiro questions why all three of them, her and her companions, transferred to the school. Ryusei Kenzaki replies that they are related. Mizuiro states that he likes Rurichiyo's way of speaking and prompts Ichigo to treat her to some juice. He is later seen going home with the rest of the group when they run into Rurichiyo and her companions.
Fake Karakura Town arc
Keigo finds Mizuiro and informs him of Sosuke Aizen's attack on Karakura Town. Keigo leaves Chizuru with him and leaves. Later, Keigo returns with Tatsuki, Don Kanonji and Michiru Ogawa. Tatsuki expresses her surprise that Mizuiro, and Chizuru are awake. Mizuiro reveals that he took emergency supplies from the dormant town, and its stores. Including food, a charger for his mobile phone, and a few stun guns. He is seen shrugging off Tatsuki's disdaining comments. Mizuiro says that the most important thing is that their lives are being targeted. After hearing how dangerous Aizen is, Mizuiro discards the stun guns, calling Aizen a cheater. When Aizen's Reiatsu suddenly looms over them, the group rise to run for their lives. Not panicking, Mizuiro calmly picks up a bottle, and throws it at Aizen when he blocks their path. The bottle disintegrates before it can hit him. Noting this, Mizuiro then rolls a canister expelling flammable gas towards Aizen.He ushers his friends away, and ignites the gas with a lighter. Engulfing Aizen in an explosion, causing Keigo and Tatsuki to note Mizuiro's methods were "insane". When Aizen emerges unscathed from the attack, the group runs. Zennousuke Kurumadani arrives, and attacks Aizen with his Shikai, momentarily trapping him. When Aizen escapes, Mizuiro and the group run away.
When Aizen encounters the group again, Ichigo arrives. He notes the members of the group, including Mizuiro, and tells them to remain where they are. He then forces Aizen to move to another location.
The Lost Substitute Shinigami arc
17 months later, Mizuiro joins Ichigo on his way to school. Chad and Orihime had informed him and the others about Ichigo's powers, and they believed it immediately. He is now in a different class than Ichigo and Keigo, and leaves. Later that day, while walking home with Ichigo and Keigo, a thief rushes by them and is being chased by the man who's bag he had just stolen. Ichigo gives Mizuiro his bag, and chases the thief down.
While Ichigo is negotiating with the sports clubs at Karakura High School, Mizuiro enters the room. Keigo tells him that Ichigo is busy for negotiating and it will last for little long. Mizuiro asks if the basketball club's rental period has ended already. When Keigo expresses his frustration that Ichigo will not hang around with him any more, Mizuiro responds that he makes it seem as if Ichigo normally hung out with him. Keigo frantically corrects him that it is not like he follows Ichigo anywhere he goes and annoy him. When they wonder why Ichigo is so concerned so much about saving money so soon and what he will do once he graduates, Keigo asks Mizuiro if Ichigo is planning to live alone. Mizuiro answers that he is not sure about that, saying that Ichigo's father is not the type who will give money to support Ichigo's needs. When they heard that Ichigo accepted soccer club vice-president Satoda's offer on being their goalkeeper, he asks Ichigo when he will start, Ichigo says that it is today.
After Shukuro Tsukishima calls him, he, Tatsuki, and Keigo arrive at Ichigo's house. He walks in and is a little surprised that Ichigo is there as well. As Ichigo and Kugo Ginjo enter Tsukishima's mansion, they are greeted by Mizuiro, and other friends of Ichigo. Mizuiro, along with everyone else tells Ichigo that Tsukishima is not angry, and then tells Ichigo he should apologize. Some time later, following Kugo's defeat and Tsukishima's death, he returns back to normal, alongside Ichigo's family and the rest of his friends.
The 10 Thousand Year Blood War arc
Mizuiro is walking with Tatsuki and Keigo, listening to their conversation regarding Ichigo's whereabouts. He deduces that, given the fact that Chad, Orihime, and Uryū aren't around, Ichigo has business in Soul Society. When Shunsui Kyoraku shows up, he recognizes him as the captain of the 8th Division. Shunsui says he is glad that he recognizes him, although he would have preferred the attention of a female. He wonders why a captain would come to them, noting that Shunsui must have a very important reason to. Shunsui confirms this and states that he has come to discuss their parting of Ichigo.
Learning that Ichigo has once again been dragged into the affairs of Soul Society, Mizuiro remains calm after Shunsui tells them that their friend may need to remain in Soul Society should his powers risk affecting the Human World. Despite Keigo's outrage, Mizuiro continues to question Shunsui about the situation, asking as to what the chances of this happening were. Being told that it was only a 1 in 10,000 chance, Shunsui explains that even if its just a remote chance, he feels that not telling Ichigo's friends about it would be unfair. Receiving a Soul Ticket from the captain, Shunsui leaves Mizuiro and the others with the promise that he'll send Ichigo home to rest before the final battle.
After the Soul King's death when the worlds start collapsing, Mizuiro responds to Keigo's comment about the lack of information regarding the apparent earthquake by saying it's probably because it's minor.
Ten years later, Mizuiro goes with Keigo and Tatsuki to the Kurosaki Clinic in order to see Sado's boxing match on TV with the Kurosaki family. Rukia and Renji later arrive, and Mizuiro happily greets Rukia, complimenting her hair growing out.
- In the Official Character Book SOULs, a part of his description says 'He has a cute face, but he's actually a ????'. At the moment, Tite Kubo has not said anything about this blanked out word, leaving it unidentified.
- Japanese : Jun Fukuyama (2004 – Present)
- English : Tom Fahn (2006 – Present)
all information on Mizuiro Kojima came from http://bleach.wikia.com/wiki/Mizuiro_Kojima