Ghost Hunt, Sakurako-san no Ashimoto ni wa Shitai ga Umatteiru Recommendations
Eerie mysteries in both animes solved predominantly with logic (although Ghost Hunt involves more supernatural occurrences). In both animes the 2 main characters are partners in solving mysteries, separated by a considerable age gap. The younger accomplice is just a high schooler, but has more potential than initially thought, while the older accomplice specializes in what they do.
If you love mystery with some horror and cool characters! Sakurako has more beautiful new animation, but Ghost Hunt has mysteries as well - they have both a modern gothic feeling