Transition
Going from a scooter to a helicopter that's big even for yourself (oneself), is a huge transition.
It's an upward transition, so that's nice, but it's still going to take you a long time to get used to using a big helicopter instead of a scooter.
せん
うつ, みやこがえ
None
You decide one transition isn't enough, so you transition to a centaur (せん) too. Now you're a big half horse-half human creature and you'll fit in the big helicopter better.
A centaur is just a human halfway between transitioning into a horse, so it isn't even that hard to do!