Hidden power typing

The particular type a pokemon gets seems to be random, but it will only ever get the one. Even if attempting to TM - when it gains Hidden Power again, it will always revert back to the same type.

Your Togekiss will only ever get Bug as its Hidden Power.

I don't know what is the algorithm to determine it, but for sure it is determined for a given Pokémon and you cannot change its type by using FTM's. If your Togekiss has Bug type HP, it will continue to be like that no matter how many FTM's you use.

you can't use a TM to change the type of Hidden Power. you can switch back and forth between Hidden Power and Air Slash, but Hidden Power will always remain with the type you started out with (ex. if you started with Bug-type HP, it is permanent).

as far as I know, there are 15 hidden power types, so likely, it just selects one at random from the 15? i honestly don't know, but that's my best guess.