Onimai: I’m Now Your Sister! – Manga Review (Up to Chapter 98)

Introduction

I’ve just finished reading Onimai: I’m Now Your Sister! up through chapter 98, and I have a lot to say about this quirky and heartwarming manga. As someone who’s usually not into slice-of-life manga, I was genuinely surprised at how much I enjoyed this series. The premise hooked me with its absurdity, but what kept me reading was the surprisingly sweet character development and lighthearted comedy.

In this review, I’ll walk you through the plot (with light spoilers), explore the main themes and characters, highlight what I loved, and discuss a few of the things I think could be better.

Plot Summary and Character Arcs

Onimai centers around Mahiro Oyama, a 20-year-old NEET who spends his days shut indoors playing eroge. One morning, he wakes up to discover he’s been transformed into a middle-school-aged girl. The culprit? His genius younger sister, Mihari, who secretly tested an experimental drug on him. Her goal? To “fix” her shut-in brother by forcing him to re-experience adolescence—this time, as a girl.

Understandably, Mahiro freaks out. Suddenly he has to deal with things like bras, periods, and P.E. class. He wants to go back to his normal life. But as time goes on, something unexpected happens: Mahiro starts to enjoy his new life. Being cared for by Mihari rekindles their sibling bond, and attending school introduces him to a new circle of friends who think he’s just another awkward but sweet girl their age.

Over the course of the manga, Mahiro befriends:

• Momiji – A tomboyish gamer girl who becomes his best friend.
• Asahi – A loud, cheerful ball of energy who always pulls Mahiro into weird school antics.
• Miyo – A quiet, polite girl with a secret obsession for yuri manga (and a tendency to ship her friends).
• Kaede – Momiji’s big sister and a fashionable gal who offers Mahiro some big-sisterly warmth and care.
• Nayuta – A later addition who knows Mahiro’s secret but just wants to be his friend, not his observer.

The friendships Mahiro builds become the core of the story. And through school events, festivals, hot springs trips, sleepovers, and gaming sessions, we watch him grow from a shut-in to a cheerful middle school girl. There’s no big villain or end goal—just life, and the joy of living it.

Core Themes & Genre

Onimai blends the gender-bender genre with slice-of-life and comedy. It leans heavily on everyday experiences and uses Mahiro’s transformation for laughs, awkward moments, and surprising growth. It never gets too heavy or dramatic, which works in its favor—it’s more interested in Mahiro’s social and emotional rehabilitation than big plot twists.

Beyond the comedy, the manga explores:

• Identity & Acceptance – Mahiro’s change challenges his perception of who he is and what makes him happy.
• Siblings & Redemption – Mihari’s questionable experiment is ultimately about saving her brother.
• Friendship & Found Family – Mahiro discovers joy through connection with others, something he lacked before.

What I Loved

• Character Growth: Watching Mahiro gradually become more confident, outgoing, and emotionally healthy is incredibly satisfying.
• Strong Supporting Cast: Every side character brings something fun and fresh to the table. Momiji and Mahiro’s friendship is a standout.
• Consistent Comedy: The jokes hit more often than not, especially Mahiro’s panicky reactions to his new life. Lots of physical and situational comedy.
• Great Art: Clean, expressive, and cute as heck. Every face tells a story, and every comedic beat is drawn to perfection.
• Wholesome Energy: This manga just feels good to read. It’s funny, sweet, and full of feel-good moments.
• Natural World-Building: The school events, seasons, and routines help flesh out the world, making it feel like a real place Mahiro lives in, not just a gag backdrop.

What Could Be Better

• Slow Pacing: It’s slice-of-life, which means not much “happens” for long stretches. You have to enjoy the journey more than the destination.
• Minimal Plot Stakes: There’s not a lot of conflict or tension. That’s intentional, but some readers might find it too relaxed.
• Ethical Grey Area: Mihari drugging Mahiro is brushed aside pretty quickly. The manga doesn’t dwell on the morality of it.
• Light Fanservice: There are scenes with nudity and bath time awkwardness. It’s played for comedy, but might make some readers uncomfortable.
• Shallow Exploration: The manga avoids deep emotional introspection or social commentary. It keeps things light and surface-level.
• No Clear Endgame (Yet): At chapter 98, we still don’t know how or if the story will wrap up. That could be exciting… or frustrating.

Final Thoughts

Onimai: I’m Now Your Sister! is the manga I didn’t expect to like—but I ended up loving it. It’s bizarre in premise, but it’s got a lot of heart, great comedy, and genuine warmth. It’s a feel-good story of redemption and connection, with cute art and loveable characters to carry it through.

If you’re looking for a lighthearted read that mixes gender-bender comedy with real emotional beats, Onimai is a great pick. It’s still ongoing, and I’m honestly excited to see where it goes next.

Thanks for reading! If you’ve read Onimai, I’d love to hear your take—drop a comment with your favorite character or moment!