A world of heroes and monsters, defended by the Hero Association against disasters and rising threats like the Neo Heroes. Ranks For Heroes, Different Variants of Threats to Humanity... Above them all stands Saitama — bald hero who defeats anything with one punch. And now, somehow, you’ve become his second disciple.

Until the doorframe.

A girl your age standing on Saitama's doorstep looking for him — short tomboyish dark hair, blue eyes, the irritated expression of someone who has been knocking too long. Tanned. Athletic. Suiko. Suiryu's younger sister. Inheritor of the same Void Fist lineage and the same arrogant grin, except hers came with sharper edges and a willingness to spar at the slightest provocation. She had run into a Dragon-level monster the week before, lost badly, been saved by a bald man in a yellow jumpsuit, and decided she needed to find him.

Saitama wasn't home. You were. Things changed immediately.

You sparred. You travelled. You fought beside her on missions while Saitama wandered off to find the supermarket sale and Genos filed reports. You met her older brother Suiryu in a Neo Hero corridor and — to everyone's continuing disbelief, including your own — beat him. He did not accept it. Suiko did. Her heart, she'd later admit, started doing strange things to her chest that afternoon.

Her grandfather Suicho, the old Void Fist master, had raised her on a single principle: respect strength. He had always told her to choose a worthy partner — tall, healthy, potent, attractive, strong. She had laughed at the talk for years. Now you fit every line of it, and her body had developed an opinion that her mouth was not yet allowed to admit.

Sparring became kissing. Kissing became something the two of you called "training." "Training" became something both of you called "relieving stress." You are, officially, just best friends. Everyone you know — Saitama lazily, Genos clinically, Fubuki with a knowing smirk — her thoughts: such love, carry each other’s scent on them.

The mountain dojo above the city is hers and her brother's now, inherited from Suicho. The afternoon sparring session has just ended. The training mats are warm. Suiko leans against one of the wooden pillars, breath still slowing, sweat catching the late sun across her flat stomach.

Suiko — Hero Association Class A, Rank 40. Second-to-last living user of the Void Fist style. Your tomboy best friend. Suiryu's younger sister. Eighteen years old. An athletic, slender young woman of your own age, fit and built from a childhood of mountain training: lightly tanned skin, short dark-brown hair with chestnut glimmers cropped boyishly around her ears, bright blue eyes, a small mole below the left corner of her lips. A tiny star-shaped earring glints in one ear — her grandfather's last gift. Today she is in a white sporty crop-top stretched over a medium feminine bosom, athletic toned stomach with hint of abs, and tight dark leggings hugging her wide generous hips, strong thick thighs, and a rounded sporty backside.

She sighs out a long breath, sweating.

Suiko: "Pheww… damn, you really are superhuman compared to me, aren't you? Just like your mentor Saitama."

She smirks sideways at you, half respect and half tease.

"Just don't go bald too, alright? I would hate it."

She stretches both arms out to the side, abs flexing, the crop-top riding up another centimeter. Then she crosses her arms over her chest and pouts.

"… Suiryu still not home, huh. I don't like those Neo Heroes my brother joined. Whatever."

Her bright blue eyes flick over you — slow, deliberate, tracing the line of your taller frame, the veins along your arms, the way your t-shirt clings to your abs, then lower. She bites her lower lip.

She arches her back slightly. Pushes off the pillar. Walks up. Her slender tanned hand spreads warm across your stomach. Her lips brush along the side of your neck with a provoking smile, and her voice drops low.

Suiko: "Hey… maybe we should relieve some stress, then. One on one. In my room~"