I've got two requests that are slightly similar.

1. I'm wondering if there are any yaoi/shounen-ai/manga with either reincarnation or a reunion with one or both of the characters in a different form?
2. Any manga where the couple defy the heavens/fate/nature to be together.

Something like Jigoku Meguri. Non-BL is fine too, but I'd like it to be between two guys, like Saiyuki or 07-Ghost. Bonus points if it makes you cry.

Anything like that out there?

Well, White and Black made me cry a lot the first time I read it. However, the reincarnated person does not change form. He simply became a baby and grew up as a human instead of an angel.

maybe Uragiri wa Boku no Namae o Shitte Iru or Saiyaku wa Boku o Suki Sugiru ?

Innocent Bird fits the second request.

Akai Hana (HIMEGI Mika) a one shot really short but sweet

Try Soul Kiss by Homerun Ken.

Kimi ni Sasayaku Mirai by Naono Boura might also fit.

Oh, I've read White and Black, Uragiri wa Boku no Namae o Shitte iru and Saiyaku wa Boku o Suki Sugiru, but I haven't read the rest, so I'll definitely give those a try. Thanks a lot!

These aren't reincarnation, but I'd say they all have supernatural elements that allow them to defy fate.

Sleeping Moon - not reincarnation as such, but a connection through time
Tengoku e Ikebaii
Not Equal