 If you liked
Katekyou Hitman Reborn!
|
 ...then you might like
Soul Eater
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Both KHR and Soul Eater has a group of main characters who are introduced one-by-one, and got together later because of some incidents. The main characters then encounter problems among themselves, and face-off with a common enemy.
Both anime also has the 'work hard/fight for the sake of their friends' theme.