Noriko Issun Moonlights as an Idol Singer
The first episode has several clues that point towards this conclusion: In the ED, Noriko appears alongside Momo with icons of peaches and mallets surrounding both of them. Later, Momo gets her own still with more peach symbolism, but Noriko doesn't get a still of her own. Instead, we see some idol with auburn hair and red eyes who is also surrounded by mallets. That same idol is seen on billboards and banners in the first episode with the name "Noririn", a cutesy Japanese pet name for the given name Noriko, and one banner even has a little mallet icon on it. In the ED, Noriko is seen sitting on the sidelines during volleyball, which could be to ensure her wig doesn't fall off. Finally, the idea of a "gap" between different aspects of a person's personality is a common trope in Japanese media.When "Noririn" first speaks in episode three, it's very obviously Miyu Tomita doing a high-pitched voice.
Noriko Issun Does Not Moonlight as an Idol Singer
By episode three, the twist is so blatant the show will instead pull the rug and reveal they really are two separate people. Kuma is Secretly the Oni Leader
King Incognito is a common trope, and the title of the show gives away that oni have a way to disguise themselves. The circumstances of Kuma's first appearance — the leader is mysteriously missing, but Eion-sama tells them to "take Kuma with you, it might help" — are very suspicious. It may be a Secret Test of Character for the onikko, or maybe s/he just needs a vacation and an excuse to get drunk. HiDive refers to the leader as "King Yama", but the Japanese dialogue just uses "Enuo-sama", a gender-neutral honorific. There Will be an Incredible Shrinking Man Episode
The fairy tale of Issun-boshi is about a one-inch boy who gets a magical mallet that allows him to grow and shrink things — including himself. Issun-boshi's descendent, Noriko, is a classmate of the oni girls, and mallets are strongly associated with "Noririn" whenever she appears, most prominently as some sort of magical girl trinket in the ED.