Nichijou o Todokeru Fujiwara-kun no Tegami ~2 Tsuume - Rikoshugi no Ryouiki to Yougashi

When Fujiwara, the head of the newspaper club, sees the shortcake that was handed out, he starts talking about a quarrel between siblings that happened once.

"Shortcake reminds me of that devilish behaviour..."

The brother and sister fought over the cake, sometimes violently, sometimes quietly.
Was it really the elder brother or the younger sister who acted in a 'devilish' manner? Or is it the sister?

"I won't accept this ending!"