That is rather a lot to absorb. Koutarou wasn't aware that Li held him in such regard, especially considering the Commander had not apparently been acquainted with him as of less than five minutes ago.
But as he is asked a question, Koutarou's mindset snaps back to that of a soldier.
"To protect ourselves. At least, in theory. Some might argue we fight Hollows so we will not fight amongst ourselves, given what little I know of the founding reasons for Seireitei.
Ultimately, each soldier has his or her own reason to fight the Hollows, but ideally, we should fight only because we have to."