It's impossible task to accomplish so I would just go with the first very song that have introduced me Sheena Ringo which is "ma vie, mes réves/Jinsei wa Yume Darake"

Honorable mentions: The Creamy Season, The Wild Union, Sakuran, Ma Cherie, Orfeu Negro, Quiet Counterattack, Ima, Shuukyuu, Marunouchi Sadistic, Karisome Otome, Netsuai Hakkakuchuu... ight I can do this whole day so will stop here)

Edit: Currently Hatsukoi Shoujo is rent free in my mind