Once again I blame the Alien for everything.
Unfortunately, the whole thing was Honoka idea, she was too naive to make a "game", she could just say that upon returning the coin one could get something miniscule but worthy, not granting any kind of wish (with a lil bit djinn shenanigans) not knowing at that time humans are capable to make really fucked up things if given such a chance.
After Honoka death, the Alien continued with her idea out of sort of pledge to her memory of pure person who died tragically.