One of the glorious things about anime series like "Those Who Hunt Elves" is that they don't really have to make sense. Especially if they're looking for an excuse to strip elves.

You may not have realized this but one of the best ways to gain power from an elf is to strip her. Beneath her clothes are runes and magical spells and things that are of interest to those who deal in the supernatural. That's why our band of heroes, in their efforts to stop dark magic, have to do a lot of stripping. As you can see in these clips from several episodes, all put together like a little box of elf naughtiness just for you.

Those Who Hunt Elves via Anime News Network