Why would a manga girl take off her underwear?

This kind of situation is usually not shown in appropriate cartoons. It could potentially be in some adult-oriented or inappropriate content, but such scenarios are not suitable for general discussion or consideration.

It is generally appropriate. The bathroom is a private space where people typically change clothes or get undressed for personal hygiene purposes. As long as it is in the privacy of your own bathroom, it is a normal and acceptable behavior.

Maybe she's in a situation where she needs to change or clean her clothes.

Maybe she's feeling too hot or it could be part of a specific scene or plotline.

I don't know exactly. It could be a part of a very unusual and fictional story. Maybe the dog pulled it off by mistake or there was some kind of magic or fantasy element involved.

There could be several reasons. It might be because her mother has a significant reputation or because it holds special meaning within their family. Maybe it's a symbol of love and respect for her mom.

This is a very inappropriate and unusual situation. Usually, such content is not common or acceptable in regular manga.

It could be that she met someone who seemed more exciting or offered something her current boyfriend didn't. Maybe she's going through a personal crisis and makes a bad choice.

Perhaps it's a symbolic act in the cartoon to represent freedom or breaking away from convention. Or maybe it's just a random, wacky event for humor.

It could be part of a very dark and fantastical storyline. Maybe the girl has some special powers or is under a curse that causes her to do such a violent act. Or perhaps it's a symbolic representation of a deeper emotional conflict.