This is a Japanese cultural trope. Whether they're a boy or a girl, a Japanese teen's first "adult" kiss on the lips is a momentous occasion. It is something to be built up to and shared with a very special person -- something that is remembered for the rest of one's life. A spoiled or stolen first kiss is an occasion for profound angst and even anger. Consequently, in any anime plotline involving teen romance, the first kiss is an important milestone in the development of both self and relationship. Compare Sex as Rite-Of-Passage. Examples of Sacred First Kiss include: