I thought the cover art was pretty eye-catching, but you shouldnt judge books by their cover because this was shit. I read 5 chapters and dropped so take this review with a grain of salt. None of the characters are interesting in the slightest. Its as if the author WANTED to fit as many flat, undeveloped, character stereotypes as possible. The only ones that stand out are the sister (the one with the biggest presence on the story so far), the detective friend (the gung-ho leader vibe and amount of presence just scream they are important), and chloe (for all the wrong reasons). The main character himself is boring, like an edgy sasuke only focused on finding their older sibling.
As another reviewer mentioned, Chloe is the worst. Not only does she insert herself into everything, but she speaks with the lamest speech quirk Ive ever seen, and Ive read homestuck: So she replaces me and you with moi and toi. It shouldnt piss me off so much but it does because not only is it super pretentious but also the grammar issues?? Like its not a one-to-one replacement ie, "toi is" if you replace it with you, it becomes "you is" which is incorrect english. It would actually be a way more interesting quirk if she just spoke full-on french and only the detective understood her BECAUSE AT LEAST THEN THERE WOULD BE SOME CHARACTER DYNAMICS.
The plot so far seems random and the "fanservice" does not fit the tone of the scene or is out of the blue.

Edit: I had my suspicions about this, but it really is the author's first work? (At least according to mal,) so I'll be less harsh with my score.