Rainy Sister 3 is encountered on floors 1 through 4 of Marukyu Striptease. It may drop 3rd Girl's Talc when defeated. Selling a 3rd Girl's Talc will unlock the Akisame Fan for Yukiko Amagi in the shop, which has the highest attack rating for fans until the Secret Laboratory equipment becomes available, but only has a Hit rate of 50.
In Golden, Rainy Sister 3 appears on Floors 1, 2, 7 through 10 of Marukyu Striptease. It may also drop Lemon Quartz and Olive Stone for trade at Shiroku Pub.