Mahou Onna ga Kuru

Summary

Sakazaki Riko, age 31 and also known as Magic Girl Collie, is lonely. Ever since she was a child, she used her magical powers of being able to turn into an adult to help people and solve cases. It has been decades since she started and Riko is now 31 years old and single. The one magic power she had is now useless as she's already a grown up. Find out what happens to a witch after her prime who goes off to search for someone special.