Plot Summary of the Chiikawa Movie | The Original Island Arc, Spoiler-Free

The Movie's Original Story Is the "Island Arc" Collected in Volume 8

The original story of the movie Chiikawa: The Secret of Mermaid Island is the Island Arc (Siren Arc), collected in Volume 8. The Island Arc is also sometimes called the "Siren Arc" or "Mermaid Arc," and it follows Chiikawa, Hachiware, and Usagi as they travel to an island thanks to a high-paying job and get caught up in turmoil surrounding a Mermaid and a Siren. If you want the manga's plot in a single sentence: it's a long adventure wearing the face of a fun island trip.

Besides the trio, the Island Arc also features Rakko, Momonga, Furuhonya, Kurimanju, and Shisa. At the destination, Shimajiro, the Siren, and the Mermaid join in as well, with many characters involved in everything from the island's welcome to the search and the curry-making.

On the original manga's X account, the arc ran as a serial from March 14, 2023 to November 26, across 130 posts. The entry point is the island recruitment notice Usagi brings. The paper prominently advertises a reward of 100 times the usual amount, and Chiikawa and Hachiware are stunned by the number. Pushed over the edge by the condition that meals are also free, the three pack their bags and head to the meeting spot by the sea. The adventure begins with terms so good you can't help wanting to join.

Other participants gather at the meeting spot, and from offshore a vehicle approaches with a white bird's neck and body as its hull. They board the vessel that appears at the appointed time and cross the sea toward the worksite—up to this point, the flow brims with the exhilaration of departure. But what awaits on the island is more than just a job briefing. A welcome feast, a nighttime cave, an unfamiliar song—events unfold that carry them gradually away from everyday life.

From the Welcome Feast to the Cave Where the Mermaid's Song Can Be Heard

Upon arriving on the island, the group is welcomed by the islanders with flower garlands and waist ornaments. The feast features island-exclusive ramen and a parfait loaded with fruit, and Shisa enjoys the sweets while pondering what to eat next. Meanwhile, Chiikawa is crouched down, apparently suffering from seasickness, and Hachiware searches nearby for something Chiikawa might be able to eat. Even amid the lively welcome, the scene retains the trio's familiar thoughtfulness for each other. It's also a stretch where a trip that began with the lure of a reward looks like a holiday spent savoring the island's distinctive cuisine.

Night eventually falls, and Chiikawa, Hachiware, and Usagi enter a cave. As the three glide across the water in a small boat, a Mermaid emerges from below the surface. The Mermaid sings about how delicious the island's food is and the joy of eating until full, and Hachiware and the others take it as a song about cooking and start singing along. Despite the dark cave and the little boat, this first encounter is remarkably cheerful.

This welcome and the song show early on that food in the Island Arc is never mere background. The pleasure of tasting island-exclusive dishes not only decorates the purpose of the trip but also connects to the turmoil that follows. Because the characters who delight honestly in good food and the circumstances lurking beneath the water are set in motion at the same time, the calmer the scene, the more you wonder what changes lie ahead. A meal where friends fuss over Chiikawa's health and the meal the Mermaid sings about are placed close together, so the same act of "eating" looks strikingly different in tone.

The Siren's Appearance and the Search Request from the Islanders

A huge Siren rises from the water before the little boat that had been exchanging songs with the Mermaid. Startled, Chiikawa and the others work the oars and try to pull away, but the Siren carves through the water in pursuit. The small boat is even shown being lifted by waves, and the joyful chorus instantly turns into a tense chase. It's a vivid turning point where the Island Arc's atmosphere shifts from journey to incident.

Afterward, the Siren informs them that one of its companion Mermaids has gone missing. Around the same time on the island, word spreads that residents are being abducted one after another, and the assembled participants are asked to subjugate the culprit. With missing companions on both the Mermaids' side and the islanders' side, you can't settle the situation on either party's word alone. Questions of who to search for and what to verify overlap and expand into a problem for the whole island. Only each side's anxiety reaches the others first, leaving an uneasiness that sets it apart from a simple monster hunt.

The island's representative explains that they are not skilled in combat and hands weapons to Chiikawa and the others. Hachiware receives a rod-like tool whose tip opens like a mouth, and equipment is prepared for Usagi and Chiikawa as well. The group, who came for a high-paying job, now finds itself shouldering the task of searching for the missing. The sight of them clutching unfamiliar weapons conveys bewilderment more than reliability, and that in turn underscores how great the danger is.

Chiikawa Searching for Friends, and Shimajiro's Shop

Armed with their weapons, the group searches for the missing, using the cave and the water's edge as clues. But while moving through the forest, Chiikawa becomes separated from the others. Walking on with fatigue and hunger, Chiikawa spots a name sign by the roadside and arrives at Shimajiro's shop, which serves shellfish soup. In the middle of an isolated search, a food shop appears like a small place of refuge.

Inside the shop, Shimajiro worries about Chiikawa, whose strength has suddenly given out, and offers curry and shellfish soup. Even while eating bite by bite, Chiikawa can't stop thinking about the friends left behind. The island cuisine everyone savored together at the welcome feast now becomes the strength to keep walking. Shimajiro's large frame and the calm mealtime restore a moment of breathing to the tense search.

Shimajiro goes further, saying he has an idea where the friends might be, and guides Chiikawa to a cave by the water. Acting on the story that an islander who went in to gather shellfish saw a Mermaid deep inside, he dives into the water himself to verify it. Even as Chiikawa worries about the danger, Shimajiro puts the waiting time of those needing rescue first. Though introduced as the shop's owner, he proves a dependable ally who moves the search forward. He doesn't stop at serving food and offering rest; he supports Chiikawa with both his knowledge of the island and his capacity for action.

Curry-Making Begins, Together with the Islanders

Based on the clues gathered in the search, Chiikawa and the others devise a way to stop the Siren. What begins then is spicy curry-making, with the islanders joining in. Kurimanju serves as head chef and Shisa as taste-tester, Chiikawa and Hachiware gather ingredients, and the islanders carry crops in from the fields. Trying to move the situation with cooking in addition to weapons is a very Island Arc turn of events, given how the arc has layered food scenes one after another. As the group welcomed as the island's guests and the islanders who welcomed them work for the same pot, the previously scattered roles of the characters converge into a single task.

The free meals promised on the recruitment notice, the welcome ramen and parfait, the Mermaid's song, Shimajiro's curry and shellfish soup—each of these connects to the big pot everyone makes together. However, what the curry changes, and how the matter of the Siren and the Mermaids is resolved, are the core parts best confirmed in Volume 8.

If you want to read a summary that keeps the core ending hidden, the Island Arc story page is your entry point; if you want to follow the original posts in order of publication, start from the Island Arc page. Those who want to binge-read the collected edition can check the volume information from the Volume 8 page. The circumstances of the Mermaid and the Siren, what happens after Shimajiro joins in, and where the curry-making leads—the more you read the surrounding posts in sequence, the more the swings between tension and humor come through.