[It's the usual speech pattern he uses when he doesn't feel relaxed around people. That being said, he slips into it now because he feels he's been rude for not properly introducing himself! He's glad Gladio doesn't take it to heart, some people know to be very touchy about it.]

It's not that complex, Japanese people tend to have complicated surnames. [That is to say- he's practiced to pick up on difficult names overall. Especially because his "mentor" was very famous and had famous clients.]

Hmm, [Yusuke shakes his head and smiles a bit,] I don't mind either way. [But Gladio calling him 'Fox' rings so good to him.] If you are used to the nickname, feel free to continue using it.