In the opening scene, we see a very young Kanata alone in an abandoned house and she is crying. She sees someone outside and it is a female soldier carrying a trumpet.
Now Kanata is older and she has volunteered for the Army and is training to be a trumpeter. There has been a ceasefire in the war and she is riding a train with several soldiers and the sergeant gives her a treat, caramels. She gets off at her stop and rides on a motorcycle up to the post in town called Seize City. She is to be stationed with the 1121 Platoon at a fort called the Clocktower Fortress. The driver stops outside town since there is a festival going on and he cannot drive through town. He points out the fortress to Kanata and tells her that she needs to get there and report in. The driver leaves and Kanata heads to Clocktower Fortress.
As Kanata walks through town and takes in the sights and sounds of the people, she looks through a store window and is startled when a young woman points at her and she runs off. The young woman is actually Rio, the sergeant of 1121 Platoon. An older woman in the store asks her what is wrong and Rio refers to Kanata as a lost kitten. Kanata stops running and a child approaches her and splashes her with colored water. Then everyone starts splashing each other and Kanata gets into the act too. Rio arrives after the excitement has died down and finds Kanata soaked to the bone. She chides Kanata for joining in and getting her uniform wet and Kanata sneezes.
Rio takes Kanata to Naomi's house so she can get a bath and get her uniform cleaned and dried. Rio tells Kanata that the festival is for the Fire Maidens that saved the city many years ago. Later, Rio says to put the visit on her tab and Naomi gives her a bell that she had fixed. She asks if it was a present from her father. Kanata chimes in that the bell is a D flat and that it is somehow familiar. While she is holding the bell outside, an owl swoops in and grabs it from Kanata. Kanata doesn't think and jumps after the bird and Rio grabs her before she falls off a balcony. Rio tells her that the bell is not important, but Kanata thinks that it is.
Later, Kanata leaves and is about to head to Clockwork Fortress when she hears the bell. She decides that she must retrieve the bell and heads towards the sound. As she follows it to a cliff above the river, Rio is dressed as a Flame Maiden and taking part in the festival. We learn the story behind the Flame Maiden legend. A fire-breathing, winged demon took residence in the valley below the town and caused the people of the town to suffer. It then kidnapped the maidens that lived in the fort and put them in a labyrinth underground and he kept them separated. The maidens refused to give up and called to each other with golden horns given to them by the Lord of Heaven. Upon escaping the labyrinth, they were helped by a giant spider and took the head of the demon. The demon then started shooting out flames and the maidens took turns embracing the head as the townspeople would douse them with water to keep the fire at bay. After a year, the flames finally died away and this is the reason the townspeople have their festival to celebrate the maidens.
Kanata is climbing down the cliff and she reaches a point on the path where she sees the bell hanging across it. She must jump to get over the gap and she does and makes it to the other side, but the path crumbles away and she falls into the water. As she sinks, she sees the skeleton of the headless demon. She swims up to the surface and makes it to the shore. She holds up the bell and thinks back to the past when she first met the female soldier that was a trumpeter. She remembers that the soldier had told her to think of her mother and she is sure that she would feel it. Kanata then blows on her trumpet and hopes that someone hears her.
As Rio finishes the ritual of the Flame Maidens, she hears Kanata's trumpet and she takes her trumpet and replies. Kanata hears Rio's trumpet and knows that they can find her now and she passes out.
Rio wakes Kanata up and Kanata asks where she is. Rio says that they are in Clocktower Fortress. They go up to the top of the fortress and Rio plays a beautiful melody on her trumpet and tells Kanata that she will teach her how to play and has Kanata play a wake-up reveille. Kanata is stunned that she wants her to play it already and she tries but it is not too good.