Rumi is Erina's master, Miru's older sister, and the leader of Rabi Rabi Island.

Friends with Irisu, Kotri, Rita, and many others; she also takes care of Cocoa.

She becomes interested in researching the Stele after her sister goes missing.

She secretly protects the island from the unknown side effects of triggering the Stele.

She actually loves bunnies a lot, but has more self-control than any of the other characters.

When researching the effects of the Stele underground (The Forgotten Cave II), she becomes affected by the magic around the place. The magic shows images of the other world (Earth) all around the cave, which strangely disturbs Rumi. Once she's freed from the remaining magic's influence, she gets obsessed with trying to find answers. She seeks out Cicini's help to figure out what's going on.