Both series are about a girl with multiple personalities. In each case, her normal personality is calm & polite personality, but sometimes her hidden identity comes out and she becomes very violent & very deadly.i
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.
Both Yankumi from Gokusen and Maki from Change series, try to live a normal life despite being the heiresses of a yakuza family. There is this one "tiny" obstacle, namely the fearful yakuza woman mode. In case of Maki its a separate personality and in case of Yankumi it's subconsciously acting the way she was raised. If you liked the yakuza setting and the heroine in one of those manga, the other manga might be worth checking out.
P.S. Change series consist of Change 2!! and its sequel W Change!!
Sachie Wakamura's mother has just passed away, making her an orphan. Suddenly, a man claiming to be her grandfather appears asking Sachie to live with him. Things aren't as simple as they seem to be when she realizes her grandfather is the boss of a yakuza gang and she is to live with him and the rest of his men. To make matters worse she is assigned a bodyguard named Rakuto, who is the handsome, popular student council president at her new school. Sachie must now try to fit in with her new family and deal with her developing feelings for Rakuto, who appears to only see her as the granddaughter of his boss. Are Sachie and Rakuto destined to continue in this master-servant relationship forever or will her feelings finally be reciprocated?
It seems that heiresses of yakuza clans who want to lead a normal life tend to develop two personalities. One is that of a normal girl and the other is that of a fearful yakuza woman. It seems to be that case in both Arakure and Change 2!!, though more literately in the Change series, since the heroine actually has split personality disorder. If you like yakuza manga, both of those might interest you. Just a word of warning, both of those contain small bits of ecchi (shoujo ecchi isn't exactly the same thing as shounen one) and the emphasis on the romance part goes through the roof in Arakure.
P.S. Change 2!! has a sequel titled W Change!! The ecchi part, which wasn't even prominent in the first manga, gets toned down even further there (which is a good thing for those of you who don't like ecchi).