He is the one who rediscovers the Bible Black in the Academy basement. Using French and Latin dictionaries, he translates the bible Black and tries some of the spells and causes Rika Shiraki to fall in love with him and the two have sex in the school gymnasium.
Reika Kitami, the school nurse and an evil witch, finds out about Taki's magic skills and is able to get a demon to possess him and make him her pawn. Corrupted by the demon and his ego over the magic he can do, Taki's personality becomes darker and he even helps get the art teacher, Hiroko Takashiro raped by Reika's followers. Kurumi Imari, Taki's neighbor and his true love interest slaps him for his actions. The slap has an exorcismal effect, freeing Taki of the demon. Reika gets angry and forces him to watch Imari get raped by her followers.
Forced to leave, Takashiro tells Taki about her past with the previous witchcraft club, the Red Cross. Taki and Takashiro have sex at that point. The next day, Shiraki stabs Minase and rapes him as he bleeds to death. Takashiro stuns her with magic and uses good magic to save Minase. It's soon revealed that Reika has kidnapped Imari and plans to transfer her soul into the young woman to avoid death due to a pact Reika made with the Devil twelve years ago. Takashiro helps Taki translate the one spell to stop Reika.
Using the spell, Reika is seemingly thwarted and sent to Hell. Taki confesses his love for Imari and the two have sex. Unbeknownst to everyone else, Reika survived and shares Imari's body. It's unknown what happened to Taki in Bible Black Testament.