Mairimashita! Iruma-kun Volume 3 contains chapters 17 to 25.
The cover features a colour print of Clara and Iruma in the background.
Chapter 17 - Clara's Mad Love
Alice observes Iruma picking classes, though Iruma's desire to take an in-class lecture due to his immense body pain and wanting to NOT move. He does walk over to Clara to see what she is taking, and both Iruma and Alice are shocked to see that she has chosen to take a Succubus lesson. Alice says that Clara is pitiful because she apparently didn't read what it said, but Clara confirms she signed up for it on purpose, causing Alice to accuse her of conspiring against them, which Clara tries to avoid answering.
It turns out three days ago, Clara told Sabro that she was jealous Iruma was playing with Ameri and she wants him back. Sabro suggested she seduce him, which is why she has chosen to take this course, fully confdent she will make Iruma fall for her.
At the lecture, the lecturer Raim says that Concupiscence is something one nurtures, and succubi will change their appearance to their partners preference, though the most important aspect is technique. After she throws Caim Kamui out after he attempts to see some 'higher-level' learning, Raim uses her Bloodline Magic Ero Scope to analyze the eros level of her students and assign ranks to them. She scans Elizabetta and records her at 89%, a Rank A. She scans Kerori and records her at 51%, a Rank B. Kerori starts to feel nervous, but Raim says that the lowest she has scanned is 21%, so compared to others she will be fine. When she scans Clara though, she is left completely dumbfounded when she sees her level is 2%. She even says that babies have at least 3% eros, meaning Clara is more innocent than a baby. She proceeds to give Clara several books to help her, calling her special.
Over time, Clara reads the books and tries to utilize what she reads. She first tries posing by stretching her legs, arching her back, and posing her arms in a heart shape, hoping to entice him. Iruma, however, thinks she is doing a new exercise, and Clara runs off to read more. Her second lesson has her try attaching to Iruma, which she does by grabbing his back. He thinks they are playing and after a short play session, she runs off. Her third lesson has her wearing a costume, but it doesn't work. Her fourth is using perfume, but its putrid smell repels everyone. Her fifth lesson is wearing makeup, but it just causes others to laugh at her.
Returning to Raim, she tells Clara she is making no progress at all. She does offer Clara an aphrodisiac to woo Iruma over, but Clara leaves and says she doesn't need it. She sits on a field with an annoyed look as Iruma approaches her, saying he was worried. Clara apologizes for her previous behavior, but is left speechless when he says it isn't safe for girls to go out alone. Surprised by Iruma's statement, she stands up and tells Iruma she will make him fall hard, which actually causes his heart to skip a beat. The two of them go off to find Alice as Raim watches from a far, scanning her and wondering what happened to her, because her eros level is now 10%.
Chapter 18 - The Battler Challenge
At the cafeteria, Iruma admires how fancy his meal is now that he is Rank 2. He notices that there aren't that many people present, but before Alice can answer, several girls approach Alice and start fawning over him, unaware they were crushing Iruma under them. He demands they get off him, where they notice his presence. One of them recognizes him as the one who made a teacher into a Familiar, manipulated the Beast of the Valley, and attacked his classmate. They back up from him out of fear, but when they think he is Rank 1, they immediately push him aside to talk to Alice again. Clara reveals to them that Iruma is now Rank 2, which they see for themselves on his uniform. They apologize for jumping to conclusions and offer to hang out with him. They then hear a sound and run off, leaving Iruma to comment how quickly they changed the pace and Alice calling them rude, though he feels is the case for being Rank 1.
Iruma asks why they left so quickly, causing Alice to remember what he wanted to tell Iruma earlier. He hangs up a flier that says "Battler". As Iruma and Clara look at it, Alice explains they are also called 'group activities'; basically students who share similar interests and skills meet with one another, and even lists some examples. He says it is a good way to improve various skills and potentially move up in rank by participating. Iruma compares it to a club, and expresses a desire to join one due to never being able to in the Human World. Alice and Clara offer to join him in whatever Battler Party he chooses if it means he could rank up. After saying that though, Iruma wonders what his next step is and if trying to go for Rank 3 would just be going with the flow again. However, now that he knows what it is like to work hard for something, he decides to participate believing he can find his true goal.
As soon as Iruma tells the two of them he will participate, Alice picks him up and puts him on a pillow on the table. He explains he brought Iruma to the cafeteria to see the beginning. He also reveals that because of seniors from various Battlers, the students do a "Rookie Hunt", where they hunt down various first-year students to join their respective Battlers in order to raise rank.
Chapter 19 - Rookie Hunt
Before the Rookie Hunt started, the teachers announce the rules of the treaty: don't bother the other hunters, don't leave the boundaries, and play nice, not carelessly. After announcing the start, several demon students run in looking for first-years for their Division. Several of them tried to approach Iruma, but Alice holds them back with his magic. Several of them try to approach Alice himself, but he repels them with his magic and even burns their cheat sheets. Iruma ends up witnessing how brutal the Rookie Hunt is, seeing various students being grabbed by ones much larger, as if they were being forced to join.
Alice says to Iruma that it will quiet down soon, because the Division that controls the student body, the Student Council, will arrive to calm things down, which it does. Iruma remembers Alice telling him the President was looking for him, but when he turns around, he is surprised to see Azazel Ameri, who's presence quells the noise of the other students. Alice reveals to Iruma that Ameri is the President, which shocks him. Ameri notices Iruma and walks over to him. Several watching believe she is approaching Alice because of how skilled he is. In actuality, she was offering a flyer to Iruma, inviting him to join her Division (in addition to having him read to her more). She walks off along with her subordinates as Iruma decides to take his leave so he can process all this new information. Alice asks if he wants to check out the other Divisions in the Classroom Tower, which he accepts.
The three of them walk around the various Divisions, with Iruma taking more flyers than he should, Alice rejecting those approaching him, and Clara taking one from the Seduction Division. The three come across Lied, Jazz, and Kamui. Lied wants to join the Game Division for strategic training, Jazz wants to join the Magical Development Division to develop new magic, and Kamui is trying to join a Female Body Division. Alice labels him a pervert while chastising Lied and Jazz for apparently just wanting to play games and steal, respectively.
Lied asks Iruma what he wants to join, saying how popular he is with the magic he has, unaware it really belongs to Sullivan. He tries to say he doesn't know, but the Ring of Gluttony starts glowing and drags him away. Iruma worries the ring is rampaging again, but it finally stops when he finds himself with his hand on the throat of another student. The two proceed to apologize to one another.
Chapter 20 - The Demon Without Magical Energy
Iruma backs up nervously when he sees blood coming out of the student's mouth, fearing he killed him by accident. The student, however, gets back up saying he fears he might have from the scare. Iruma asks about the blood on his mouth and the student says he has always had a weak body, so it happens a lot to him. The student notices the ring on Iruma's finger and deduces it reacted to his collar because they are made from the same material. He notices all his knocked over equipment and he starts picking them up. Iruma tries to apologize before noticing other students looking at the boy