If you liked
D.Gray-man
|
...then you might like
Hangyaku no Kage Tsukai
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Having something (shadow in Hangyaku, akuma in DGM) that can take over a body, some mysterious enemy that creates/initiates this taking over. Main character fights against that. Main character pretty badass.
If you liked
Bloody Junkie
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...then you might like
Torikago no Tsugai
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Torikago no Tsugai and Bloody Junkie both involve a survival game in a closed area, the difference being that Torikago no Tsugai revolves around pairs, whereas Bloody Junkie is more of an individual case.
If you liked
D.Gray-man
|
...then you might like
Kuroshitsuji
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Having watched Kuroshitsuji right after finishing D.Gray-Man, a few "common terms" were noticed, though in very different contexts. "Akuma" -- Demon. The enemies in D.Gray-Man, and one of the protagonists of Kuroshitsuji. "Hakushaku" -- Earl. Referring to both Ciel in Kuroshitsuji and the Millenium Earl in DGM. Also, both have young protagonists with a "cursed" eye, and many characters. Also Allen and Ciel both are half in the "white" and "black" worlds.
If you liked
Nurarihyon no Mago
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...then you might like
Yoru to Yakusoku
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Both talk about half-youkai, half-humans who deal with passing off as humans.
If you liked
MÄR
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...then you might like
Rekka no Honoo
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Both by the same mangaka. The main characters both have similar principles, in the way that they view their friends. Both Ginta and Recca fight for their Hime's (princesses), are aiming towards beating a strong enemy, gather a group of strong people, and fight in tournament-style fights. The antagonists are also organized in similar ways in both series, with ranks. The Madogu and the Arms are also very similar in the sense that they are different and weapons. Both characters' relatives and friends are similar as well.
If you liked
Cristo
|
...then you might like
Crimson-Shell
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The protagonists of each series (Kei in Cristo and Claudia in Crimson Shell) have similar relationships with the antagonistic groups (Adys in Cristo and Black Roses in Crimson Shell)
If you liked
Death Note
|
...then you might like
Zennou no Noa
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Both Raito (Light) and Noa have very similar personalities, and the paths to their power are similar. When I read Zennou no Noa, I had this nagging sense of seeing Raito in there. Both characters are very intelligent, and able to read far ahead when planning. Both mangas are very good reads.