The Wallflower, Volume 13: Yamatonadeshiko Shichihenge

CURSE OF THE DIAMOND Sunako just wants to remain in seclusion inside her dark room, but glam Auntie has other plans and drags her niece to a party. Upon arrival, Sunako takes refuge in an empty coffin, where she finds a diamond. Imagine morbid Sunako's delight when she learns the jewel is cursed