I noticed the misgendering too but honestly I thought the translation was pretty decent otherwise.
As for the love at first sight and their relationship as a whole, out of spoiler I’ll just say, if you’re looking for healthy, normal, relationship dynamics, this ain’t the story for that.
I read the first light novel & webnovel because ‘scary assassin devoted to one person while still remaining completely unhinged around everyone else’ is like my guilty pleasure trope catnip—and in that sense the story delivers—but I’ll tell anyone who is uncomfortable about the age gap and interest displayed in this chapter that it isn’t gonna get dialed down.
Yes, he’s obsessed pretty much right away. Early arcs, it’s kind of like ‘an adorable pet bunny rabbit I want to pamper who is cute precisely because I could crush her at any moment and she still sits in my hands’. And that obsession is mutual on her part pretty quickly. They are wildly codependent. In a like, ‘keep poison on hand in case one of them dies so the other can follow right away’ and ‘it’s cool if you kill me, but no one else can’ kind of way. At one point I remember just accepting they were both nuts and rolling with it. FWIW it does at least get clarified across the early webnovel arcs that he isn’t physically interested in her, but even with that caveat… they get informally engaged in like, the next chapter—when she is five, just to hammer that home—for reasons that are politically convenient to the folks who agree to it, and then formally engaged when she is 12 and married when she’s 16, and the plan—which she is 100% on board with—is for him to whisk her away and keep her pretty much confined in a mansion and estate away from everyone else. So…know what you’re getting into if you keep reading?