Souta Mizutani thought it was unbelievable that the beautiful, intelligent Shino Aizawa approached him and declared that she loved him. However, that quickly becomes the least unbelievable part of the situation, when three more Shino Aizawas appear to declare Shino's love for Souta as well.
Shino explains - she had been running a bit late for school, and was taking a shortcut through woods to get there quickly. However, the ground gave out beneath her feet, trapping her in a sinkhole. After a few hours, she resolved herself that she'd never just be passive again and would confess to Souta (her long-time crush) if she were ever to get out. Just then, a duplicate of herself manifested in front of her, and the two worked together to get out of the hole. The other two that had appeared manifested as Shino confessed, and now the four want Souta to go out with Shino.
Aizawa-San Multiplies (Aizawa-San Zoushoku in Japanese) is a comedy about what happens when one person is literally a harem all by herself.
This series has examples of:
- A-Cup Angst: Shino is only modestly endowed, and she's a little frustrated (though usually only Shiki expresses it) at that fact. All of her duplicates, as well as the original, show varying levels of jealousy over Ozeki's ample development.
- It goes even further than that: Shino and her duplicates have bust sizes that differ by about 1-3 centimeters, with Shiki having the largest, followed by Yuki, then Hami. Upon finding this out, Shino can only pause and find relief in that she's still bigger than Tomoko. She's also a little too interested in how she compares to Anna, her black-haired fifth duplicate.
- Cannot Spit It Out: It's soon revealed that Shino wanted to confess to Souta for two years before the start of the series. She even named a cat after him because of it.
- Cloud Cuckoo Lander: Shino herself - she'll regularly do things like wear shoes on the wrong feet or just completely space out. Her first thought about how her life could change with her duplication power? Become a stand-up comedian. Mrs. Aizawa is similarly a bit spacey, throwing out whatever silly excuse first pops into her head as to how to explain where all of the extra duplicates came from (her idea for Yuki was that she grew up in an RPG-Mechanics Verse).
- Covert Pervert: Most of the Aizawas, except for Shiki (who is in no way covert about it).
- Date Peepers: Nakamura, Ozeki, and Shiki watch Shino and Souta's first date to make sure it goes along well, though they resolve to leave once they see the two holding hands.
- Determinator: Yuki (the duplicate from Shino's resolve and courage) is not one to back down when she wants something. Based on the fact that Shino finally starts a relationship due to what transpired after Yuki's manifestation, she's becoming more of one as time goes on.
- Disaster Dominoes: Begins to tip when Souta and Aizawa go to where she first manifested Yuki, to see if they could dispel the three duplicates. Aizawa gleefully jumps down the pit because Souta is above and can just pull her up with the rope. When he goes to do so, they discover that the answer to dispelling the duplicates isn't down there... by pulling up a fourth duplicate.
- Genius Ditz: Shino - top student in the school, excellent athlete, complete Cloud Cuckoo Lander.
- Heroic Seductress: Shiki, based on Shino's libido, is not at all subtle about wanting Souta and Shino, together, with clothing optional.
- How We Got Here: Chapter 12 ends with Souta telling his friend Nakamura that he's in love with Shino, and Shino suddenly revealing her presence as he says this. Chapter 13 shows what led up to her eavesdropping on him.
- Literal Split Personality: Each duplicate is based off of Shino's emotional state when they first manifested.
- Love Confession: First panel of the manga. And several more in the first chapter, from the duplicates. Souta doesn't properly answer until the second chapter.
- Open-Minded Parent: Aizawa's mother just immediately goes into "care for children" mode when Shino finally is forward with her duplicates. In fact, due to the fact that Souta accompanied all of them for the conversation, Aizawa's mother was most interested in finally meeting Souta, though she does say that part of that was that the duplicates weren't all that good at hiding from her in the first place.
- Power Incontinence: Shino has absolutely no control over when a duplicate will manifest or merge back - the duplicate does. Inverted in chapters 17 and 18 - Yuki suddenly finds herself unable to remerge with Shino.
- Puberty Superpower: Aizawa's mother says that all the girls in her family get some variety of power when they're teens, which is why she's not terribly surprised at the fact that she went from having one daughter to having four.
- Secret Keeper: Aizawa's power is kept secret by Souta and his childhood friend, Chika Ozeki.
- Self-Duplication: Shino's power, which she can use to practical effect (such as when she escaped from the hole where her powers first manifested).
- Shipper on Deck: All of the duplicates want Shino and Souta together, and they're all vocal about it.
- Theme Naming: Souta (who gets picked invariably by Aizawa for the task) names the duplicates based on the personality trait they embody. Yuki for her courage, Hami for her shyness, Shiki for her lecherousness, and Tomoko for her childishness.
- Two-Person Love Triangle: Expanded upon - all of Shino's duplicates share her base wants and desires, so Shino and her duplicates all love Souta. While he sees them all as different people, they share experiences so there is no conflict; his relationship is with all of them indirectly.
- Unwanted Harem: While they overall root for Shino to be with Souta, the duplicates are still based on Shino's mind and desires, so they too want some time with him.