as kids mashiro, was also a friends little sister to him. when the two and her older brother was at a festival they climbed a tree to get a better view of the fire works. but mashiro could not climb. so Mc got off the tree and stayed with her.
so now they are again at a festival. and she wants to show him that she has grown. so she climbs the tree. but her alethic stats are bottom tier, so it took lots of attempts. but she eventually did it covered in dirt.