Rumia is a youkai that can manipulate the darkness but judging from her Embodiment of Scarlet Devil appearance she is only powerful enough to make it seem like late evening. Apparently she is quite simpleminded but isn039t featured in enough conversations for details about her personality to be revealed. Rumia039s hair ribbon is actually an amulet. She can039t touch it so she can039t take it off. In the events of Embodiment of Scarlet Devil she039s attacked by the heroines for no reason probably just as a general warmup and has nothing to do with the main story. According to comments about her in the Bunbunmaru Newspaper and in Perfect Memento it seems that she039s constantly surrounded by a mass/blob of darkness at all times except during the new moon and so is rarely actually seen in person. Despite her innocent appearance she eats humans. Source: Touhou Wikia