[Spoilers for the game below]-----------------------------------
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1) You can spot that dear sweet prince if you go drinking with Kadokura (he's the bartender at the bar).
2) The Halloween party should happen unless you tell Yuusaku to fuck off or tell Kadokura that you refuse to plan the party. Even if you just say "yeah, I'll plan the party" and then do nothing else related to it, it will still happen (it just won't be a very good party lmao).