Hana Ni Arashi is a 2 volume manga series by Takagi Shigeyoshi, started in 2006.
Plot: Riko Kunimi is trying to lead a normal high school life when Ran Tachibana bursts into her classroom carrying a gun and tells her that her life is now his. Ran, the richest, most powerful 17-year-old in Japan, wants her as his wife, and he's not taking no for an answer!
- Source: Baka-Updates