Shibariya Komachi manga summary:

Chiko is a high school student who can see other people’s red threads, or the thread that connects one person to his/her soul mate. She uses her ability as a musubi-ya to advise her schoolmates on their love lives, for a fee of course! But upon stumbling upon a hidden room at her school, she sees a mysterious looking white spool of thread that suddenly comes alive and traps her. The next thing she knows, her body has become like a ten-year old kid again and the only way to get back her body is to use the mysterious thread to expel evil spirits and become a real musubi-ya!