Missile Happy! 

Mikako, our over-zealous heroine, has a sister-complex so strong she won't let just any man wed her sister. On an undercover investigation to learn more about the newest bachelor, she ends up moving in with him! Plus the guy is a highschool kid just like her! Mikako's relationship with him starts to grow. What'll happen between Mikako and him?! (Source: TOKYOPOP) Notes: Chapter count includes the one shots Sentimental Kajou (Overly Sentimental | センチメンタル過剰); Senaka no Kare (The Boyfriend Beside Me | 背中の彼); Koi no Dorei (Slave of Love | 恋の奴隷) and Egao Kakumei (Smiling Revolution | 笑顔革命), the mangaka's debut story.