He's there to kill her, but then realizes a weapon alone doesn't make a threat when you're/it's that small. He is trying to be a good assassin, but is just not suited for it. They become allies, and instead of trying to kill her, he starts just trying to annoy her at worse, but mainly just endeavors to help her however he can since she's his Mooncap now (a faerie assassin guild command rank). She doesn't care about the little pesterings because she likes his company and learning about the faerie world that rejected such a well-meaning fellow. But when it comes to past debts and obligations, distraction alone doesn't make an alibi when you're/it's that small...