While that may be true for Gilbert, he's fighting a very steep uphill battle with Kiju's opinion of him just because of what he is. She views anything that carries the taint of abyssal influence as being malicious decievers at best and mindless bloodthirsty abominations in general. So far Gilbert is living up to her expectations of such beings, at least in the malicious deciever sense,  in the way he hides his true identity both in appearance and name as well as attempted an assault upon her before attempting diplomacy while still bearing arms. Of course, given her history with abyssal creatures in general, Gilbert never stood any real chance of gaining any measure of trust from her.