I'm almost 100% sure that this manga was only shounen-ai, rather than yaoi. The main characters lived in a place where two people were born with "partners" or something like that. They needed each other to live because one of them contained too much energy in their body, while the other contained too little. The one with too much energy would regularly give some to their "partner" through a kiss. I think the one with too little was sort of a cold character, while the one with too much was very friendly. The friendly one had a foreigner as a friend and, since the foreigner was interested in the whole "energy" concept, kissed him to show him what it was like. Sorry if my explanation is confusing! 😐

Maybe Shinkuu Yuusetsu?

Hrodulf and Bjornolfr, you will not be forgotten.
[img]http://i411.photobucket.com/albums/pp199/SyberAngelGabrielle/couplesig.jpg[/img]
[color=black]And if the world were black and white,
you would be my rainbow in shades of grey.[/color]

Click 'n Play!

If I had a fantasy self, it'd be a tentacle monster.

Quote from NightSwan

Maybe Shinkuu Yuusetsu?

That's it! Thank you! 🙂