Just unlock all the portraits for all characters, this is a fantastic game I like it a lot, your arts remind me of Dagasi & moki, but with more cuteness style, which is your own style!
But there is one thing about gameplay that kinda annoyed me, the level progression, from lv1 to 2 takes a lot of times, but with level increase, leveling become so easy but with increasing difficulty, it's fair since the difficulty is up, but if I'm unlucky or made mistakes & failed, I have to go through that long long lv1→2 process again, which is kinda annoying.
But still, I love this game a lot, remind me of Monster Mind, although it's totally different type of game.