I have none to recommend(other than Kenshin or Shaman King) but I can tell you now that Bleach is not for a twelve-year old boy. It has quite a few crude comment and in later chapters, undetailed nudity and some partial nudity. Several of the female characters are over-endowed and only one (usually) has the decency to cover herself. The blood and violence might also be too much for your brother to handle(I know I wouldn't let my brothers read it). Every character who fights spills enough blood to have died twenty times and are still walking around. There is also a very perverted lesbian.
Oh yeah. I haven't seen the nudity yet, but you may want to check on this first. There are quite a few crude comments (namely from the lesbian and Kon).