I've read somewhere that there must be an NPC for it, but I can't find it. And the same problem with Oreko.
.flow version 0.18, English.
Tried it myself.
In the school, first room if I remember correctly, the individuals behind the counter change your theme from those that you have.
Also got the flower theme from where that respectively is, and an NPC does give it to you.
Version 0.18 English.