 If you liked
GTO
|
 ...then you might like
Shinjuku Swan
|
If you love Onizuka Sensei, you'll love Shiratori...they're like brothers.
Both series explore some of the darker sides of society and have great themes, but Shinjuku Swan goes very dark, but can bounce back to the lighter tones.
Unlike GTO here there are real villains/antagonists...and they are very twisted in their own ways