Vivarium De Choushoku Wo

Vivarium De Choushoku Wo summary:

The manga centers on three sixth graders, Yoshiki Obana, Mikoto Tajo, and Kikuri Kushida, who meet up at morning to get to the bottom of their town's "seven mysteries" as a free summer vacation project. After finishing one meeting at their "secret base", Yoshiki meets a mysterious ghost on his way home.