Mars by Fuyumi Soryo (15 volumes)
One of the most stunning pieces of romance I've ever read. The plot follows the story of Kira Aso: a normal high school girl who has plain looks, a shy personality and has few friends, and Rei Kashino: a rebellious high school boy who flirts with all hot girls, rides his motorcycle everywhere and lives in poverty on his own.
The two high schoolers meet at a park close to their homes. Kira is there drawing pictures of the people walking around. The wind blows some of her pictures away from her and Rei, who just happens to be there, helps her pick them up. Noticing that one picture portrays a mother holding her baby child Rei's facial expression becomes slightly sad and he comments on how he never knew a mother's love. Both think nothing of their first encounter, but... it was just the beginning.
Later, it seems that whenever something happens to one, the other is close by... at the right place at the right time. Eventually, a love sprouts... a love tainted with forbidden juice since Rei is poor, a slight manwhore, dangerous and daring while Kira comes from a quiet, soft home.
Of course, the plot isn't all love and heartwarming stories of fluff. Both Kira and Rei have their own dark pasts and haunting experiences which tie them even closer together as they experience what love is and how when you fall into it, there's no getting out.
Non-plot wise, Mars has beautiful artwork that's quite unique to the artist. Each panel seems to have been created with care and hard-work. The characters designs fit the character's personalities and the flow of the story.