...and I bet the manga is too. The main character here is a guy who apparently wants to minimize his involvement in the life around him. He's not a creepy loner, but just someone who would rather conserve his psychic energy as much as possible. Anyone who has experienced much manga or anime will know that this is an attitude that just wouldn't do in Japan! "Do your best!" Is their incessant motto, and so as I started watching the anime of this, I was surprised the show didn't have him being bullied or some such thing.

No, it's not that at all. Rather, this is the story of how such a guy can gradually become interested in the world around him. How? Well of course, factor number 1 is a girl, although that doesn't become apparent for a long time. Almost as motivating, factor number 2 in drawing him out is a great group of friends. Factor number 3, finally, is a mystery from the past. This mystery reveals its existence to the group of friends slowly, and the MC takes a leading part in figuring it out. It's a terrific mystery, in my opinion, and not one viewer/reader in a thousand will be able to figure it out before the end.

Overall, what we have here is a well-written story of growth and maturation, played out by a cast of interesting, smart characters, and presented subtly and intelligently.

Nice. It is actual detective stories, not supernatural stuff.
But, I really don't like the protagonist. And sometimes there are big, at least for me, plot holes.