Mushi Monogatari

Thirteen years ago, Yoh's mother suddenly disappeared without coming to pick him up from daycare. Even now that he is a high school student, Yoh is still traumatized by his mother and his own birthday. When his childhood friend Kanoko wishes him a happy birthday, Yho evades the call by saying "there are swarms of mosquitoes" and runs away. When Yoh returns home alone while his grandmother, with whom he lives, is away on a trip, the person waiting for him there is... his mother, who disappeared on his birthday thirteen years ago!

(Source: Hakusensha, translated)