My next review is a Manga only work that shows a unique relationship between it's Gender Swap victims, this is Mahou Shounen Majorian.

Iori is a timid, feminine boy. Masaru is an aggressive boy who leads the other boys in bullying Iori. One day, they encounter a pair of strange extraterrestrial bunnies who turn them into magical girls in order to fight aliens that are invading their town but Masaru isn't totally on board with being turned into a girl but is given no choice when the only way to turn back is to beat the aliens together with Iori.
Now there are factors in this show to consider, the first one being that the boys are young say about 8-10 years old at most and they are being transformed into I guess 16 year old teenage girls judging by their Magical Girl forms.
Now the main premise is that Masaru bullies Iori for acting girly, so the situation of the alien invasion and the Magical Girl stuff gives him a taste of what it feels to be an actual girl while Iori doesn't seem to mind being a girl at all. It really gives interesting takes on how two different types of personalities take to being turned into a girl.
The overall message the manga is obviously trying to give is that you shouldn't bully males who are more feminine by nature just because the norm is to be tough, like sport and I guess in some circles be an obnoxious jerk. In forcing Masaru to work with Iori both as girls forces the two to bond together, while Masaru tries to resist fiercely as it breaks apart his whole persona as a school bully but eventually by the end he respects Iori for who he is and that's quite a powerful message. It's actually quite surprising how little this manga is used to promote zero tolerance on bullying.
As this is Manga only, obviously no Anime.
Final Verdict: An obscure title that has deeper meanings you need to search for in order to appreciate the message it's delivering but it requires patience and a lot of digging up through Manga Scan sites to achieve that, otherwise study Japanese and find the Manga yourself.