Rainy Sister 1 (霧雨姉妹の長女, Kirisame Shimai no Chōjo) is a Shadow in the series. It only appears on rainy days.
Rainy Sister 1 appears in B1F and B2F of the Secret Laboratory within the Midnight Channel on rainy days. After being defeated, it may drop 1st Girl's Talc. Selling the 1st Girl's Talc will unlock the Niagra Climber male armor in the shop, which has moderate defense for Secret Laboratory armor and low evade, but comes with an Auto-Rakukaja effect.
In Golden, it appears in B1 to B4. It may also drop Meteorite, Rose Quartz or Buffalo Stone.