Hunter x Hunter
Both are long adventure stories that start approachable, then gradually reveal darker rules, smarter power systems, and morally complicated arcs. Fans of Brotherhood's mix of comedy, tragedy, worldbuilding, and tactical fights usually find a lot to like in Hunter x Hunter.
D.Gray-man
The overlap is the gothic shounen setup: young fighters, cursed powers, religious imagery, tragic enemies, and a war that is bigger than the main cast understands at first. D.Gray-man is messier structurally, but it carries a similar blend of dark fantasy and team-based action.
Magi: The Labyrinth of Magic
Magi has the same sense of a colorful adventure world hiding serious political and historical conflict underneath. Fans who enjoyed Brotherhood's country-spanning journey, ancient systems of power, and idealistic leads facing corrupt empires will recognize the appeal.
Soul Eater
Soul Eater shares the school/team structure, supernatural combat, eccentric comedy, and darker lore that slowly creeps in. It is less tightly plotted than Brotherhood, but the bond between weapon-users and partners gives it a familiar emotional core.
The Seven Deadly Sins
This gets recommended because it also follows a fantasy team with legendary powers, kingdom politics, big reveals, and a mix of goofy comedy with serious battles. It is more straightforward battle-shounen, but fans looking for a magical adventure ensemble often understand the connection.