So Junior losing his eye wasn't due to some grand battle or moment of misjudgment it's just because Yotaka was jelous as fuck.
That being said it seems she was harboring some sort of hostility towards him for a while seeing as how Junior still had his eye during their first encounter with Snake where he was coincidentally holding a bag of ice cream, my guess is that she took his eye right after this encounter.
Didn't really expect Yotaka to have actually done it on purpose but the way she sees it she looks back at those ice cream binges fondly, so I wonder if Kanetsuna was lying or giving his own interpretation of events to Todororoki.
I swear this series reels you in with the promise of a hot lady but keeps you invested with these characters who actually have depth behind them. Be it as may I still want these two to end up together because look at them (lots of cute Yotaka moments in this chapter and that's always a plus).