The Duujin trio, which trio is that one again? 

Also, I had a random idea. Sacred fire is the signature move of Ho-oh, but also Entei can do this. And due to heritage Saruya can as well, but it's move she can't really use like her regular attacks. It's more of an instinctive use. The random thought that came up is that if the rainbow fire comes from Ho-oh, would it also enable the fire Pokémon to learn Sacred Fire, but as an instinctive move rather than a conscious move?

The idea behind the feather is that Ho-oh doesn't lose feathers often, but he is a bird so it can happen. And occasially he, as a legendary, just gets the feeling it might be time to let go of one of his feathers and will pluck one out for the wind to carry it to someone. And Ho-oh being Ho-oh, he might just decide to let one feather travel for fun, knowing humans will be excited to find it. 

Michael actually has one of Ho-oh's feathers; his father found it on one of his travels and gave it to his son as a good luck charm. That's how Lytse came in contact with it.