Moro is one of the two girls who guided Watanuki into Yūko's shop. It remains unclear whether they were created by Yūko, Clow Reed, both, or someone else entirely. However, since they lack souls and cannot leave the shop, it can be inferred that they were created there.
In chapter 126, Yūko explained that Maru and Moro must remain inside the shop to keep it in existence through their concentration. This effort results in them experiencing prolonged deep periods of sleep. They assist around the shop but primarily serve as cheerleaders. They almost always speak in unison or nearly so. Watanuki generally gets along with them, except when they drag him into one of Yūko's schemes.
Maru and Moro’s full names are derived from words meaning "exposing oneself in public," akin to "flashing" and "streaking" in English. This could be a pun on the 'xxx' in xxxHOLiC. While the 'xxx' in the title is meant to act as a variable, their appearance evokes the 'XXX' synonymous with pornography, likely intentional given the seinen audience.
There are few instances where Maru and Moro appear in serious scenes. In the parasite angel chapter, Watanuki invited them to join him at a festival, but they responded in unison (with a dazed look), "those without souls cannot leave this place... for their bodies will disintegrate."
Despite often annoying Watanuki, they show concern for both Yūko and him. In volume 6 of the manga, after Watanuki returned from visiting the "lady in the park," Maru and Moro immediately sensed something was wrong. When he collapsed, they dragged him to the shop's gates, saying, "This is as far as we can go," before tossing him out to a waiting Dōmeki. In the anime, Watanuki also shows signs of slight affection towards them; in episode 18, when Dōmeki read a letter from Mokona and Maru/Moro, Watanuki was pleased to see they thought of him.
