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.
In the summer of my third 
year of middle school...
في صيف عامي الثالث
...في المدرسة الإعداديّة
im Sommer der neunten Klasse, …
el verano de tercero de secundaria…
el verano de tercero de secundaria…
pendant l’été de ma troisième…
nell'estate della mia seconda media...
No verão do meu terceiro
ano do ensino médio...
летом моего девятого класса…