Yoichi is a former student in the M.L.S. He wears a red shirt (or sometimes white) with black pants. His hair colour is black, shoulder-length, and he wears a headband on top to move his hair back. He wears a black sweater and black pants with ear muffs instead of his headband during the Winter time. He has gray eyes and black pupils.
Yoichi is somewhat of a womanizer, and is popular with the female Magic Law students. He likes to grab girls' breasts (particularly Nana's) and is able to determine their bra sizes simply by grabbing their breasts.
Besides this, he can be extremely focused. Known for his skill, he is called the "Prince of Magic Law" by some. He can be annoying sometimes but he is also a smart judge, as he plans his attacks in at least one second or two. In that time, he can set up a decent trap or plan but this is because when he noticed Muhyo's skill bloomed, he kicked into high gear.
Yoichi appears to have a crush on Nana. However, underneath this exterior resides his experience and wisdom that rival Muhyo's. Yoichi had offered to be Muhyo's partner, but Muhyo had already chosen Roji instead. Yoichi is an expert at every type of Magical Law except for Execution. It is also shown that Yoichi has become smarter and faster since Muhyo's talent bloomed.
Yoichi was originally a student in the M.L.S, with Enchu, Biko and Muhyo. His teachers were Rio Kurotori and Page Klaus. Yoichi was especially fond of Rio because of her large breasts. He usually stayed in M.L.S with the other students but he was mostly with Muhyo and Enchu. He liked to play games unlike Enchu, who always studied and did his homework. He wasn't a smart student in the MLS, like Muhyo. They were both average. Without Enchu, they couldn't get their work done. Once when their teacher got angry at them for tardiness, the three were asked to solve a puzzle. Yoichi couldn't solve the question, nor could Muhyo, but Enchu solved in a few minutes and got them all out of trouble.
Yoichi liked Enchu a lot and considered him one of his best friends alongside Muhyo and Biko. He tried to stop Enchu from going into Forbidden Magic Law but failed to notice his friend's grief and insanity before it was too late, costing him his friend. When he went to the Association for help, Page agreed to help him search for Enchu. Since the beginning of the manga, Yoichi never stopped working in the investigation for Enchu for 2 years. He found common ground with Muhyo and the two often shared information about Enchu even while Muhyo was practicing.
Return to M.L.S.
Muhyo and Roji return to M.L.S. when Roji gets a letter regarding his examination to get promoted. Yoichi is there to greet them but Nana intrudes and knocks him under her. He doesn't mind this and just takes advantage of the situation to grope her breasts. Later, at the examination, Yoichi is the first infected with the panic curse Enchu puts over the academy. Nana ends up being infected by Yoichi's touch and she then infects Roji, who panics and sets off the curse's hysteria. In the madness, Yoichi ends up getting his neck wounded. After the chaos ends thanks to Muhyo, Roji feels guilty and inadequate and so runs away. Yoichi chases him and gives him a pep talk, explaining his, Muhyo, and Enchu's past. A flurry of vengeful ghosts summoned by Enchu attack the entire town so Yoichi sends Roji off to Muhyo. When Roji lingers, Yoichi grabs him and angrily makes it clear Roji was chosen over himself to be Muhyo's assistant.
Yoichi is assigned a new case by Page, which lists Rio as a traitor. Unwilling to believe it, Yoichi goes to Rio's house only to find it burned to the ground. Among the wreckage, he finds her diary and weeps as he reads of his teacher's descent into the Forbidden Magic Law. He then goes to try and find Biko. Despite the efforts of her students, he bursts into her study and finds an envelope with Rio's handwriting and Biko's talisman stamped with the mark of the traitor.
He realizes the urgency of the situation and so makes speed for the magic prison where Muhyo, Roji, Biko and Rio are. Yoichi arrives in the nick of time to ward off a fireball about to incinerate Biko. He helps Roji carry Biko and Muhyo into the nearby woods to hide from Rio. To buy time for Biko to brew a tempering restoration potion, he sets up a six directional circle ward against Rio's Hellfire Lizard. The brew is successful and Muhyo subdues Rio with Anesthetic Needles.
The group recovers Rio and Muhyo suggests trying to kill the Envoy with which Rio has a contract to save her soul. In the midst of setting up the ritual, no one notices Rio had a magic circle nearby active. Enchu appears and tells Muhyo it's too late to save him. Yoichi stalls Enchu and Muhyo tries anesthetizing Enchu. The attempt fails since Enchu reveals he's lost most of his humanity and so the spell loses its effect.
The Writ of Passage
When he was looking for the Writ of Passage from Isabi with Page, he lead the team
Invasion of M.L.S.
When it came to taking down Buhpu and defeating his puppets, his partners were Judge Imai and Assistant Judge Ginji. He made all the plans at the lat minute so that he can prove it to Enchu that he didn't have to be an Executor to save his mother, he could've done it as a Judge, so he made Kiriko summon Hellsquitos to spit out the truth about the Cortlaw family. Once they save Enchu, Yoichi was sad that Enchu has to live in the Arcanum and didn't want to say goodbye to him. He still tries his best so that one day Muhyo will accept him as a partner.