Deltarune Fun Fact:
At the end of Onionsan's conversation in Chapter 2, they will ask you to come back tomorrow to learn about the music they hears from the lake. However, they don't appear in Chapter 4. The player is told not to expect Onionsan to appear this chapter, both from Susie saying "your weird friend is busy today" and the strange bird-like NPC from the library saying "don't wait". Then in Chapter 5 you can find this same NPC serving "fried dough balls", which Susie says taste like onion.
This suggests that in Chapter 4 Onionsan was busy making their signature takoyaki for the festival, which the bird NPC hands out as Onionsan is too big to fit in the stall. They must be good friends :)
