Click FIREWORKS button before 18:00, it'll tell you which bombs you need to have in your inventory. You need to get 4 different types of bombs, 3 each. You can craft the bombs, or you can simply buy them from Xer's stall if you invited Xer to the fair.
There are no ENDINGS for characters, there are only certain subplots that can end already. You can check them in event log in the game.
Also, you can jump on discord and ask for tips in #guide channel