I -- okay, never read the Loveless manga, but I saw the anime, and Soul Eater handles the symbiotic relationship in the fighting pair in a really different (and usually healthier!) way. I'm really loving it a lot, based largely on the way the primary weapon character (whose name is Soul Eater) understands the relationship he has with his master (that's them in this icon). He's really...matter-of-fact and honest about the depth of their bond and what it means to be somebody's weapon, and it sort of critical hits a whole range of my buttons. :3
...I picture Shinjiro and Akihiko learning to make their souls resonate together and I am a very happy little animal. ^_^