At school, Daisuke hears that some girls have mysteriously disappeared. Later that night, Riku gets frustrated with Risa’s constant infatuation with Dark, and retires to her room, only to disappear. Daisuke’s grandfather, Daiki, figures out that a Unicorn from a cursed painting may be kidnapping the town's girls and sends Daisuke out to seal the Unicorn. Daisuke tries to save Riku (and now Risa) without becoming Dark, but is stuck when he needs to use magic to enter the painting. He calls Dark, who rescues the kidnapped girls and then tries to kiss Risa, which Daisuke forbids him to do.
A pair of policemen on night patrol are stopped by a thick fog at night. The fog spreads throughout the town, reaching the window of a sleeping child. When her mother enters, calling for her, the room is empty.
At school, Daisuke Niwa practices warning Risa Harada about Dark. However he has no chance to tell her when Risa enthusiastically thanks him for the previous evening, prompting Daisuke to flee and nearly transform.
In the restroom, Takeshi Saehara tells him about numerous girls disappearing from their locked rooms.
Inspector Saehara continues the investigation, stating that there are no clues except for a unique sound heard in the fog, which is expected to return that evening. The police are not the only ones investigating though; in a dark corner of the library, a journalist, Yuki Suzaki, studies a book on the Cultural Revolution. She questions why no one seems to remember this significant event.
Daisuke walks dejectedly down the hallway before he is dragged into a classroom by Riku Harada who blames him for not guarding Risa properly and thus enabling Dark to speak with her. Daisuke is distressed to hear what Dark did that night but is soon put into a headlock by Riku when he “spaces out”. Riku suddenly asks whether Daisuke could be Dark, causing them to both remember the forced kiss between Riku and Dark. Daisuke admits nothing but quickly apologizes anyway and flees. Riku wonders to herself why Daisuke fears her.
Catching his breath in the hallway, Daisuke reassures himself that Risa is the girl he loves and Dark cannot change that. As Daisuke jogs away, Satoshi Hiwatari observes him in secret.
That evening, in the Harada mansion, Risa cheerfully considers clothes for her date while Riku sits on the couch, unhappy about the situation and worried for her sister. Riku leaves and lays on her bed in the dark until a bright light illuminates the room. A white, winged unicorn stands before her, knocking her unconscious and carrying her on its back into a portal. Risa enters the room to find it empty and a thick fog outside outside the window. Elsewhere, Daiki Niwa prowls the streets at night, suspicious of the fog.
Fresh out of a bath, Daisuke answers a phone call from Risa, who cries while police speak with her family’s butler. Daiki then explains the origins of the disappearances to his family. Emiko wonders aloud if the unicorn is an artwork created by “that family”, but Daiki says there are no records of such a creation. Daisuke agrees without complaint to steal the artwork and is determined to use his own strength rather than Dark’s. Daiki approves but provides him with a black feather in the event that Daisuke needs to transform into Dark.Several policemen and cars gather outside the home of an old man, Mr. Nishizawa, who tells inspector Saehara that he does not own the painting that Dark’s notice describes. The inspector decides to keep the castle under surveillance anyway. As he leaves, Saehara asks two other officers where Commander Hiwatari is and concludes with a smirk that Satoshi gave up after three consecutive days of fieldwork.Nishizawa watches a police car depart from his window and says to himself that the painting should be stolen. On her balcony in the fog, Risa worries for her sister.
Daisuke finds a way around the patrol cars, relieved that he can still open a hidden door in a brick wall. He must swim 400 meters underwater to reach the entrance, which is longer than his record, but his determination to save Risa’s sister pushes him forward.Daisuke emerges through a fountain in the castle’s courtyard. He sees the unicorn flying above with Risa on its back and runs after them, but it disappears through a portal. He breaks into the building and sees them in a large painting on the wall. Try as he might, he cannot enter the painting and cries in frustration at his weakness. With no other choice, he looks at a photograph of his love and transforms into Dark.Nishizawa turns on the lights in the room, ordering Dark to steal the painting. Sadly, the man admits that he painted it with all his heart when his daughter, Misaki, was still alive. She died in a tragic accident when he finished the painting, and the pain caused him to lock it away.
Dark, wielding the black feather, activates its magic with a German spell and enters the painting. He tries to shake Risa awake, but she tells him not to interfere, having already entered into Misaki’s feelings. Misaki asks the unicorn to remove Dark, however the sight of him in pain frees Risa from the spell.
Risa begs Misaki to stop, as the paradise that the unicorn has given her is fake. Misaki refuses; she has waited so long for everyone to join her party that she can no longer count the lonely years that have passed. Risa implores her, crying that the children who have been stolen are lonely too.
Dark summons With with his feather, entrapping the unicorn in a portal and freeing the children. Dark grabs her hand when Risa hesitates to leave Misaki, and reassures her that the latter will no longer be lonely. Misaki waves farewell at the departing pair.
Back in the castle, the old man tends to the saved children while Dark flies away with Risa in his arms after Riku accuses the thief of being a pervert. Above the city, Dark brings her to a cliff of wind turbines and tries to kiss her. However, he is stopped by Daisuke’s distress and submits to his wishes this time.
The next day, people from around the town, including Risa and Daisuke, flock to the castle to see the newly displayed painting of Misaki and the unicorn.
- The unicorn’s hooves sound like a glass instrument that was used by 19th Century Italian opera composer, Donizetti.
- “Harada-san! Did Dark say anything to you last night? No matter what, don’t trust anything he told you.” - Daisuke Niwa
- “Could Dark possibly be Niwa-kun?” - Riku Harada
- “Just as I thought. Now that I’ve become aware of him…” - Satoshi Hiwatari
- “Even in a miserable situation like this, that feeling reacts… My love genes... Come out, Dark!” - Daisuke Niwa
- “Ich möchte helfen!” - Dark Mousy
- “Everyone has been separated from their parents and can’t see them anymore! Even their beloved friends. You understand, don’t you? That feels lonely…” - Risa Harada
- “Bye! You can go home on your own.” - Dark Mousy