"Umaru and Her Student" (うまると弟子, Umaru to Deshi) is the 3rd episode of the Himouto! Umaru-chan anime series. It was produced by Doga Kobo.
The day before a big test, Umaru procrastinates. She then has a nightmare about failing (the nightmare consists of Umaru being in the military, fighting against test questions). When she wakes up, Umaru tearfully begs Taihei to help her study, and it pays off as she gets another perfect score.
Umaru wonders about Kirie staring at her lately. She then imagines what would happen if her true self was discovered (she imagines Kirie's anger towards Umaru, leading to them and Ebina eventually settling things and, along with "Komaru", riding on Umaru's now-giant hamsters, then flying in space). That night, when she hears someone at the door, she wonders if it's Taihei bringing food. Instead, she encounters... KIRIE!
Umaru begins to freak out over Kirie discovering who Umaru really is; however, Kirie finds Umaru's real form cute, and asks if she's Umaru's sister. Umaru comes up with a fake name: "Komaru". Kirie reveals that she has been following Umaru around and returns Umaru's student ID. Kirie asks "Komaru" if she could call her "Mistress." Taihei returns and is terrified by Kirie. Umaru discovers that Kirie is extremely shy unless she's around children.
Umaru and Taihei watch a scary movie and Umaru, although she claims she isn't scared, is utterly freaked out by it.
umaru's classroom is 1-A
Kirie's "menacing" is a reference to JoJo's Bizarre Adventure.
Gacha is a used in many successful Japanese free-to-play games (it's gambling technique uses a reel or more which spins when a button is pushed).
Umaru: "Playing an FPS isn't playing around! I don't play around! I DON'T PLAY AROUND!!!!!!!!!!!!!!!!"
Umaru (crying): "Onii-chan, help me study!!!!!!!!!!!"