So Ash is about to be on his 5th female travel companion

[CaptainJigglypuff]

^8th female travelling with him if you count temporary companions. You forgot about Cheryl. She went with Ash in Eterna Forrest for three episodes back in Sinnoh.

Anyway, maybe Serena won't care Pikachu will destroy her bike (if she HAS one) since it's implied she and Ash are already good friends. A good long time friend wouldn't let an accident that has happened more than once ruin their friendship nor hang a guilt trip over their friend's head about it.

[precita]

Ash has had so many female companions that the ones in the middle are going to wind up forgotten. Already Iris seemed to be the least popular of all the girls, but a lot of people are starting to forget about Dawn as well even though she had a fanbase. When Serena leaves her character will wind up sandwiched in the middle too.

It's called, "middle child syndrome," where things in the middle tend to be forgotten. I think the only reason May escapes this is because she was the first new main girl of the series, so she'll always be remembered for that reason. The others really don't have this luxury especially since every girl leaves after a single gen.