He can be the joker we need.

how heavy of a spoiler is this? I wanted to play it

It's not really a spoiler. It is something that happens near the beginning of the game.

It's covered in the first 10~20min or so of the game, and is really a minor side point.

Off topic, put P5 as a game doesn't really care about spoilers much, there is one specific story telling gimmick that will screw with you if you're really sensitive to these kind of things.

If I am not mistaken, it's even shown in the marketing materials to build suspense.