Here is the full list of all 12 Iwaihime achievements.
Complete "Iwaihime: Celebration Princess".
Complete "LCSC's Great Days".
Complete "Toé Kurokami".
Complete "Tsubakiko Harumiya".
Complete "Kanae Minobe".
Complete "Riria Nunokawa".
Complete "Rokugamihime: Rokugami Princess".
Complete "Kizuatohime: Scar Princess".
Complete "Utahime: Song Princess".
Complete "Maboroshihime: Illusion Princess".
Complete "Noroihime: Curse Princess".
Complete "Musubihime: Union Princess".