With summer heat at its most relentless, there’s no better antidote than a mermaid anime full of splashing water and non-stop laughs. As part of a summer holiday special, we’re shining a spotlight on Seto no Hanayome (瀬戸の花嫁) — a 26-episode TV anime series that first aired in April 2007 and is now available to stream for free for a limited time.
From Manga to Screen
The series is based on the manga of the same name by Kimura Taihiko, serialised in Monthly GanGan WING and Monthly GanGan JOKER. Director Kishi Seiji and series composer Kamiesu Makoto teamed up to bring the story to life as a full-throttle slapstick romantic comedy — one that starts throwing jokes at the audience from the very first frame of the opening sequence.
Story: Saved by a Mermaid, Now You Have to Marry Her
The story follows Michishio Nagasumi, an ordinary middle-school boy who nearly drowns while swimming in the sea during summer vacation. He is rescued by Seto San, a cheerful and airheaded young mermaid. The catch? Under mermaid law, if a human discovers a mermaid’s true identity, one of the two must forfeit their life.
To sidestep this grim fate, the two agree to get married and move in together, attending the same school as a newly-wed couple. But the chaos is only just beginning.
San’s family home is the headquarters of the Seto-gumi, the founding clan of the Seto Inland Sea Aquatic Life Federation — in other words, a yakuza family made up of fish-people. These swaggering fish-folk keep showing up to cause mayhem, even going so far as to infiltrate Nagasumi and San’s school as teachers. To make matters worse, Edomae Runa — a rival mermaid who also happens to be a top idol — arrives on the scene, bringing her own faction, the Edomae Marine Kanto Aquatic Life Association (essentially a rival mafia), and triggering an all-out gang war.
What Makes It Great: Sharp Gags and San’s Irresistible Airheadedness
The show’s greatest strengths are its rapid-fire comedic timing and the wonderfully expressive reactions San delivers whenever her natural airheadedness kicks in. Episodes 1 through 13, set during the summer, are where the seasonal atmosphere is at its most vivid. Because young mermaids have unstable transformation abilities, even a splash of water is enough to revert San’s lower body into a fish tail — and yet she seems magnetically drawn to every body of water she encounters, much to Nagasumi’s despair. Just hearing the sound of water is enough to make viewers feel a little cooler.
Music: “Romantic summer” by Momoi Haruko
The opening theme, “Romantic summer”, was written, composed, and arranged by Momoi Haruko, the voice actress behind San, who is also an accomplished music creator. She performs the song alongside Nogawa Sakura, the voice of Runa. Momoi also contributed music to the Picture Drama and the subsequent OVA series. A standout OVA track is “梯 -Kakehashi-“ — a moody, dramatic ballad that offers a striking contrast to the retro-pop sound of “Romantic summer,” drawing listeners deep into the show’s more emotional side.
The Emotional Payoff: Episodes 12 and 13
The most talked-about stretch of the series is episodes 12 and 13, in which San and Runa go head-to-head in a battle for Nagasumi’s heart. Up to that point, San had seemed like someone who married Nagasumi purely out of obligation to the rules. Runa’s arrival forces San to confront her true feelings — and Runa herself realises she has quietly developed feelings for the boy she had been treating so dismissively. The result is a genuinely dramatic climax that proves the show is far more than just slapstick.
It is precisely this balance of comedy and heartfelt drama that has kept Seto no Hanayome beloved by fans to this day. And from episode 14 onwards, the chaos only escalates further.
Where to Watch
All 26 episodes are currently available free of charge on the official Anime Times (アニメタイムズ公式チャンネル) YouTube channel. The limited-time stream runs until Monday, 24 August 2026, at 16:59 JST. Don’t miss it.
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