If you're looking for manga similar to Boin Tantei vs. Kaitou Sanmensou, you might like these titles.
Hanuma Kyou gets visit by the god Karma-chan. Karma-chan's mission is to solve the declining birthrate in Japan. How can Kyou help her with that?
Eratarou Kamegashira is a normal guy. All he wants is to live his high school years in peace and tranquility, hopefully making a girlfriend or two in the process. However, his brother Maratarou is a gigantic pervert. Due to Maratarou's shenanigans, Eratarou has been having trouble making any girlfriends due to being associated with him. However one day, the beautiful Takahara-san asks if she could visit Eratarou. Will Eratarou be able to keep his cool and win the girl, or will his brother cause things to "heat up"?
An explorer's adventure in search of the ancient civilization of Atlantis inside a little girl's room.