Hana ni Kamiguse

In her sophomore year, Suu, an aristocratic loner with zero friends, dreamed of experiencing a typical youth. Then, one day, a handsome young man named Yuki appeared. He, a mysterious boy with amnesia, became her first cherished friend. But things might not be as straightforward as they seem!

(Source: Kodansha, translated)

Note: chapter count includes one extra chapter.