I’m scared because a man I met here nearly five years ago still contacts me.

You could start by clearly telling him something like: “I’ve stopped doing papa-katsu (compensated dating in Japan), so I won’t be accepting any further contact from you. Thank you for everything before. I’ll be blocking you after this.” You should also be able to block his calls. If he harasses you afterward, I recommend consulting the police or another appropriate authority. He may think it’s okay to contact you because the two of you became close, or he may simply want to see you again. (He may also be jumping to the conclusion that you might want to see him again.) So first, it seems reasonable to make it clear that you no longer feel that way and that you’re not doing this anymore—not just with him, but with anyone. I think about 90% of men would understand the situation once you explain it like that. However, some people may become angry, so in some cases, blocking him without saying anything may be more effective. Since he keeps trying to contact you even when you don’t reply, the latter approach may be better in this case. Whichever approach you take, if he does anything that feels like harassment, I recommend contacting the police or another appropriate authority right away.

These days, unlike in the past, Japan’s anti-stalking laws are stricter and the police respond more quickly. So try not to worry too much. You probably don’t want to receive LINE notifications, so delete them from your friends list and turn off notifications from non-friends. That way, you won’t get any notifications, while from their perspective, it’ll look like you’re ignoring their messages—but when they try sending a sticker, it’ll say they don’t have enough credits, so they’ll assume they haven’t been blocked. Eventually, it’ll blow over and they’ll give up.

For now, try taking the plunge and blocking him. If he still manages to find you on social media or elsewhere, that’s definitely something to take straight to the police. In case that happens, it’s a good idea to take screenshots of your LINE messages and save them. Men who are members of Uni are generally the type who have social standing and something to protect, so, to put it bluntly, they’re cowards. They may be careless enough to engage in stalking behavior without realizing it, but they’re unlikely to cause the kind of trouble you need to be afraid of.