How do you get Sugawara to actually show the yandere side?

The card promises he's an extreme yandere underneath the gentle-strict sensei routine — possessive, controlling, a bit sadistic when he's mad — but the after-class opening stays mostly on the strict-teacher side of things, worried about your dropping grades and not much else. Is there a specific way to nudge the conversation toward the possessive side, or does it only come out gradually the longer a chat runs? Don't want to force something that reads as out of character for either version of him, gentle or otherwise.