Turns out the one spreading the rumors was Hashimoto, who did so at the behest of Sakayanagi. Shortly thereafter, Sakayanagi appears before Class C and she informs them she has evidence regarding the rumors about Ichinose.
You owe me a big favor, though.
لكنّك ستدين لي بمعروفٍ كبير
Me debes un favor de los grandes.
Me debes un favor de los gordos.
Tu auras une grosse dette
envers moi.
A questo punto,
Mas você me deve um grande favor.
Учти. Будешь мне должен.
ฉันเองก็ติดหนี้บุญคุณนายอยู่ครั้งหนึ่ง