Not only is Illya prone to seasickness, but he has allergies and is prone to colds...don't forget his dislike of dogs too. Poor boy. I've used the seasickness trope in a fair few stories as well as Napoleon's love of sailing on the sea...but not being in the water. His fear of water I related to in a backstory where he nearly drowned as a child.

Using aspects of the actor's life and personality helps flesh out the characters, making them even more real and believable.