If you want a good yakuza (type of Japanese Mafia) manga mixed with romance and action and good plot, read Tokyo Crazy Paradise.
Its set in the near future of Japan, when crime runs rampant and everyone needs to know a little self defense just to get to work and home in one piece.(One Piece, hahaha... ah.)
The story revolves around Tsukasa(girl) and Ryuji(very hot guy), with Tsuakasa acting as Ryuji's bodyguard. He is the third generation leader of the Kuryugumi, the yakuza group. His father was assassinated just previous the start of the story, and Tsukasa and her three brothers were just recently orphaned. Tsukasa has been raised as a boy by her parents, her mothers reason being that it was too dangerous for a girl to live nowadays, and that she needed to be strong and never be beaten by a man. Both her parents were cops, and their deaths were due to inter gang disputes.
Through a series of hilarious occurrences, Tsukasa ends up being the bodyguard for Ryuji. He knows she is a girl before she knows he knows. They grew up being rivals, a cops kid and a yakuza kid, but he saved her from drowning once, and he had to take the chest guard that kept her breasts hidden off to resuscitate her. He kept her secret, and now keeps her at his side due to depts he forced her to incur.
This is a shojo manga, and probably one of the funniest I have ever read. Ever. I still laugh my head off when I read it, and I have read it like three times. I fell off the bed laughing so hard once. I have no witnesses, so you will just to have trust me. Its hilarious.
This manga has really good plot development and a lot of sneaky twists. It definitely keeps you turning, and the character progression is superb. I love that word. Its so fancy.
Tsukasa is a strong heroine, funny and headstrong, who doesn't back down on her beliefs or a fight. She is a strong shield for justice (in her words) and is loyal to a fault. Ryuji is the cold, intelligent leader of one of the strongest yakuza groups in Japan, and has a lot on his plate. The only person he finds he can be himself around is Tsukasa. Only him, his two other bodyguards(who play a key role in the story) and her family know who she really is, but she causes a stir in the yakuza world. Both of them (and those around them) find out new things about themselves, things they like and things they don't. Things change and time passes, realizations and dreams are made.
A good story all around. And keep an eye out for a certain tall dark and handsome cop ;) yum.
ps. I have notice two different spellings of the word shojo/shoujo. I will use both intermittently.