Space Brothers

The year 2006. Two brothers, Nanba Mutta (age 12) and Hibito (age 9), happen to spot a UFO headed for the moon. The experience inspires them to make a certain promise.

With his mother's assistance and Hibito's encouragement, Mutta has been accepted for the New Astronaut Selection Exam. However, unsure of his next step, he visits Sharon, who works at a nearby observatory. After receiving advice from Sharon, Mutta is finally able to make up his mind.

After advancing to the second exam, Mutta realizes that the other applicants are much better prepared than he is. Desperate to prove himself, he stakes everything on the lung capacity test, as he has confidence in his trumpet-trained lungs. However, as the other applicants drop out, he finds himself in a heated battle with Itou Serika. Who will come out on top?

After a long week, only the final interview remains in the second JAXA exam. Mutta is drawing attention as Nanba Hibito's older brother, but he insists he won't spend his entire life as Nanba Hibito's big brother.

After completing the second JAXA exam, Hibito invites Mutta for a free trip to Houston, Texas, through NASA's family support program. Upon arrival, he finds himself chased by a pug named Apo, and is then reunited with Hibito. However, Hibito expresses disappointment.

Mutta has arrived in America, but he's off to a rocky start with Hibito. Meanwhile, his future as an astronaut is in jeopardy because the headbutt incident has been brought to JAXA's attention.

Recap episode. Mutta recalls how he first got accepted for the JAXA training program.

Recap episode. Hibito recalls the ordeal of his accident on the moon.

As Mutta and his teammates try to keep warm in the cold desert night, Mutta is reminded of recent events.

The astronaut candidates have reached the sixth, and final, day of survival training. But Mutta is down with a fever. Can Team E complete the training?

After completing survival training, the NASA astronaut candidates are tasked to participate in the upcoming Comeback Competition. Each team receives an advisory engineer, but Mutta's team is stuck with someone who won't help.

As Azuma makes his way towards the moon, Mutta's team works on testing the rover, learning of what flaws they need to fix. The team consider following another team's example and going with a glider instead of a ground rover, but Pico points out that the wind would cause issues with that plan. Using his engineer insight on how to overcome their obstacles, Mutta suggests that they make the rover's tires out of sponge, so they can have larger tires that still fit inside the rocket whilst also reducing costs and providing shock absorption. Impressed by this idea, Pico decides to give the team advice on their parachute, encouraging them to think of the rover as a spaceship containing their comrades. With Mutta's ideas and Pico's advice, the team manage to put together a working rover complete with a functioning parachute. Later, as Mutta is invited by Pico for a drink, Vince takes him for a drive.