It is 1862, and the Expulsion of Foreigners movement is started by the Choushuu clan. Kusaka Touma is a member of this clan, but is at odds with his clan, and supports the Open the Country movement instead, which movement endorses peace and open borders. While trying to stop other Choushuu from setting fire to the British Embassy, Kusaka is confronted by a Bakufu (Shogunate) samurai who helps him and a comrade, Aizawa, escape from authorities.

Years later, as he tries to find a school that will teach him English, Kusaka reunites with the samurai who saved his life, Akizuki Keiichirou, who recognises him and eventually offers to secretly teach Kusaka English. However, despite precautions, a Choushuu eventually sees them together and they must stop meeting.

Kusaka considers abandoning his clan. The Head Administrator, Sufu Masanosuke, offers to send him to London to learn about the West. Before leaving, Kusaka meets with Akizuki one last time and they declare their love for each other. While Kusaka is in England, Akizuki gains the leadership of his clan. After four years, Kusaka returns to Japan and receives a high ranking post in the Imperial army. During this time, Japan is in the midst of the Boshin War, with Kusaka on the Satsuma-Choushuu (Imperial) side and Akizuki on the Bakufu (Shogunate) side. During one of the last battles, Kusaka finds Akizuki about to commit seppuku after having lost a leg to cannon fire. Kusaka is forced to kill a comrade who sees him aiding Aikizuki.

Four years later, Kusaka is working for the new government, wearing Western-style clothing and living in a Western-style home. In a private Japanese cottage behind the house, he keeps Akizuki in secret. The relationship has deteriorated, as Akizuki cannot stand being kept in hiding in comfort while his fellow Bakufu comrades suffer in prison, and he wants to commit suicide.

Eventually Aizawa, now an officer of the new law, discovers their relationship. He confronts Akizuki, leaving him with a short sword. A while later, it seems things between Kusaka and Akizuki are being patched up. Soon, a small group of police goes through Kusaka's home, led by Aizawa. Kusaka runs back to the house, engages in a brief argument with his former comrade, and returns to the cottage only to find Akizuki missing and a suicide note on the futon pillow.

Akizuki pulls himself along the snow-covered ground, the short sword in hand, stopping in front of a tree split into four trunks. After a brief reminiscing, he kills himself; Kusaka finds him a short while later. Opening the pouch around Akizuki's neck, he realizes that Akizuki was carrying around the shell of the cicada they had seen about eight years earlier. Kusaka takes the short sword from Akizuki's hand and commits suicide as well.