I had a bit of trouble coming up with an answer on this Ask. I thought about it for a long time, before eventually just letting Killua voice my thoughts on the matter in his own words. I’m not 100% sure what the asker was hoping for in a response, but I think Killua sums things up well here. Killua and Gon are good friends, and they help each other out mutually. So it doesn’t feel quite right for Killua to just, like, do something for Gon to thank him.