Check the "related" tab on MangaDex, in particular: https://mangadex.org/title/3c0dddc9-d6da-4aa5-8ed2-12d26a6b08d4/gokugoku-futsuu-no-fuufu-no-hanashi
I mean, if Pina's "love potion" played no role in what happened to Emi, then why was it a thing at all? It must have had at least some influence on people's actions, or else nobody would care. I think Pina and her potion bear some responsibility for what the boys did, even if only a little...
The one thing Waguri-san adores more than cake is seeing people smile. Beautiful soul.
And Tsumugi-kun is just as delightful. "Doing something for other people's sake is fun", indeed.