D.Gray-man, Karneval (TV) Recommendations
both have a white haired protagonist (with a black haired "friend"),involved with some mysterious power and organization fighting the evil.
Both anime have organizations fighting formerly human monsters (Akuma/Varuga) created by an enemy organization (Noah/Kafka). The organizations have several branches with eccentric leaders that mentor the main characters. The members are regularly dispatched on missions.
Both anime have a white-haired boy protagonist.
Some common positive themes are strong will, friendships, and the wish to protect loved ones. But there are also darker motifs such as despair and grief over death.
Both animes have an organization (Black Order and Circus) working for the government for the greater good. They also have similar goons the akuma and Varuga which come from innocent people being turned by the antagonists. In both the only known way to save the people is to ‘purify’ by kill them. The powers held by the characters are honed through the organization, and only those compatible and capable can use the weapons. The weapons are honed through training in D Gray Man and school in Karneval. Kanda is very similar to Gareki, both being a bit tsundere but eventually becomes friendlier to the
Both protagonists are young white-haired males (D.Gray-man's Allen Walker is 15, while Karneval's Nai is of an unconfirmed age) with some sort of secret, in a way. They are both searching for someone important to them (both of which are mentioned only a few times and in a vague manner) with the help of members of an organization attempting to rid the world of destructive monsters (the Black Order in DGM and Circus in Karneval). A few of the characters they meet are at first unfriendly (Gareki and Kanda) as well as very friendly (Lavi and Yogi). In D.Gray-man, the Akuma can take on different
Both anime have a focus on the supernatural and an organization meant to deal with it. Both are somewhat dark/sad and have their own arcs in the overarching story. Both fit into very similar genres and are both enjoyable to watch, they will both keep you hooked.