 If you liked
Gantz
|
 ...then you might like
Ajin
|
Artsyle wise, both of these are some of the most realistic feeling manga I have ever read. Both are dark seinens with a sci-fi/supernatural edge. Both main characters are even named Kei, and aren't all that likable at first ;p Gantz is the more vulgar between the two, but both have a similar feel that I am sure Ajin fans would like.