Riku

Lore & Background

Riku grew up in the shadow of a father who was once the most feared assassin alive but now spends his days stocking shelves and making onigiri. He has no memory of the violence his father left behind; to him, Sakamoto is simply Dad — the man who hums while cooking, who gets scolded by his mother, and who sometimes gets a little too serious when a stranger walks into the store. That gap between who Sakamoto was and who he is now is the emotional axis Riku unknowingly orbits. His personality is defined by restless, childlike curiosity. He asks questions that adults find awkward, pokes at objects that look dangerous, and treats every new person with the same unguarded friendliness. This makes him both the source of the series' gentlest comedy beats and, in the most tense moments, the reason a fight can't be walked away from — because the child is standing right there, watching. Narratively, Riku anchors the 'days' in the title. The story is not just about assassins; it is about a family trying to be normal. Riku's presence forces every conflict to be resolved in a way that keeps the kitchen table safe, the bedtime story intact, and the small boy's trust in his father unbroken.

In Their Own Story

The convenience store is quiet. Fluorescent lights buzz over rows of canned soup and discount chocolate. Riku sits on a small stool behind the counter, legs swinging, tracing the barcode on a bottle of melon soda with one sticky finger. His father is in the back, restocking. His mother is on a phone call, voice low and serious.

A man in a dark coat steps in. The bell chimes. Riku looks up, eyes huge, and tilts his head. 'Are you lost, mister? It's raining outside.' The man doesn't answer. Something in the air shifts — the mother's voice cuts off, the father's footsteps stop in the back. Riku doesn't understand what's happening. He just slides off his stool, grabs the man's sleeve, and says, 'Dad, this guy's here.'

And just like that, the quietest Tuesday of the year becomes the loudest.

Reader's Guide

Riku is the Sakamoto household's young son, first appearing in the early chapters as part of the domestic setup that defines the series' tone. He is a small, energetic child — pre-school or early elementary age — whose primary 'combat style' is accidentally walking into trouble and asking questions nobody wants to answer.

His personality is pure, unfiltered childhood: curious, affectionate, slightly chaotic, and completely oblivious to the danger his father's past can bring. He treats everyone with the same open warmth, which makes him both endearing and a liability in high-stakes scenes.

Key relationships center on his parents. His father, Sakamoto, is the retired assassin who now prioritizes family above all; Riku is the living reason for that choice. His mother is the grounded, no-nonsense force keeping the household running. Together they form the 'normal life' the entire plot is trying to protect.

Narratively, Riku serves as the emotional stakes made flesh. Every fight, every conspiracy, every rival who shows up at the store carries a subtext: keep this child safe. He also provides the series' gentlest comedic relief — the child who calls a loaded gun 'a shiny thing' or tries to befriend a rival assassin. The contrast between his innocence and the lethal world around him is what makes Sakamoto Days feel like more than an action manga.

Did You Know?

• Riku's presence is the primary narrative reason Sakamoto can't simply walk away from conflicts — the child is in the next room, and that changes every calculation.
• The convenience store where the family lives doubles as both a workplace and a home, meaning Riku's daily life literally overlaps with the setting where most action sequences unfold.
• Riku's innocence is used as a deliberate tonal counterweight: the series shifts between high-octane assassin battles and a small boy asking why the sky is blue, and that contrast is central to the manga's identity.
• Despite the series' violent premise, Riku is never depicted as a combatant or trained in any way; his 'power' is entirely emotional and narrative.