Yup, Teacher is the Strongest!
As a result of absorbing Eucliwood's mana, Haruna now experiences the same pains Eucliwood usually faces when speaking and being expressive. As the second day of the festival goes underway, Haruna throws her mana-absorption device away while Yuki has her ring confiscated by the teacher. At the end of the festival, the same teacher reveals himself to be the fairy Ayumu had met, a Masō-Shōjo named Chris who was Dai-sensei's mentor, who had used Haruna's device to absorb enough mana to undo a curse placed upon her. After launching the entire class into the sky, she manages to beat Ayumu before escaping with everyone's mana. As Dai-sensei gets word of Chris' revival, Kyoko offers to make a deal with her.