@PinkMage
It was actually confirmed waaaay back in Chapter 10
Page 16, panel 2 there are a bunch of Ema at the shrine the Colors are visiting and there are Ema written by basically all the main characters in Bocchi.
Teru wishes she could be a better teacher, Bocchi wishes to be friends with everyone, "Leader of the World" Aru want s to not let anyone down, Sotoka wants to be a ninja, Nako wants Bocchi to stop vomiting, and a mystery one (probably Kako) wishes to stay a figure with good morals.