1. Why is Natsu the only Dragon Slayer with motion sickness?
2. Why is Wendy immune to motion sickness?
3. Why do the dragon slayers have cats?

Why is Natsu the only Dragon Slayer with motion sickness?

It has not been explained, but it is likely due to a side effect of the Dragon Slayer Magic. Wendy’s Magic does not affect Natsu because he built up immunity. This was specifically stated by Wendy herself. Also, Happy doesn’t affect Natsu because Natsu doesn’t consider Happy as a vehicle.

Why is Wendy immune to motion sickness?

Ergo, Wendy does not get motion-sick because she is a female dragon, and female dragons are too graceful to be seen lying on the floor in a heap and puking their guts out.

Why do the dragon slayers have cats?

They are basically just pets/partners. Natsu’s cat, Happy, was found in an egg when Natsu was much younger. He thought it was a dragon egg and so he raised it with his best friend at the time, Lisanna. When it hatched, Happy came out.