Warui Mushi

Story

Commit a sin, and a "bug" attaches to you! Misao is a young boy who can see the "bugs" that attach themselves to people who have committed sins. Small bugs for minor sins, large bugs for grave sins... Through these bugs, Misao is able to measure the weight of a person's sins. However, he gradually begins to see bugs that defy these rules, and at the same time, strange incidents start occurring around him...

Synopsis via AniList (English).