3.194 out of 5 from 326 votes
Both have a high school setting with a strong lead male character who like their homeroom teacher. B Reaction is more focused on fighting whereas it's not very regular in UnbalanceX2. Although not quite a harem there is more than one girl who is after the male protagonist. B reaction is a bit short but definitely worth reading if you liked the excellent UnbalanceX2.
Both manga\manhwa revolve around a rather strong highschool student who has a crush on a (female) teacher at his school. Oddly enough, in both series it's highly indicated that it's actually not a one side thing. Unbalance x Unbalance is a bit more serious (and with lots of drama) than the other series, but there are only a few action scenes. On the other hand B.Reaction! is filled with action and fights. Not to mention, not only is the teacher strong, but she is actually stronger than protagonist. If you liked one of those two series (or the f.teacher x m.student theme) then you should definitely give the other one a try.
Yamaguchi Kumiko is next in line to be the boss of the Kuroda Ikka yakuza clan due to her parents' death. However, fresh out of college, Kumiko decides to pursue her lifelong dream of being a teacher. Now hired as a mathematics teacher at an all-boys school, Kumiko must hide her true identity. She's assigned to class 3D, inhabited by the worst of the worst delinquents. Popularly called "Yankumi" by her students, she tries her best to gain the respect of and offer help to these students who'd like nothing more to make her life a living hell.
While I believe Gokusen to be the better one of those two, I can't deny that the two of them do share a few themes. In both series we have a male student and a female teacher who can kick some ass and again in both there is something romantic in nature sparking between those two. Do I need to say more?
P.S. Too bad B.Reaction! was axed, before it got anywhere.