Shinkuu Yuusetsu, a shounen-ai manga (not yaoi) remind me of Loveless... The the partners are matched at the age of 3 or 4 based on their wavelengths. They need to be close to each other physically and they feel the best sensation when they are together. They usually live together for the rest of their lives.Just like Loveless, compared to fighters and sacrifices; there are suppliers and receivers (reminded me of uke-seme though) they exchange power by kissing.
It is not in my top-best manga list, but I just like the idea... Knowing that there is a person who you are compatible 100%, and knowing that, this person only wants to be with you too.
