Ginjiro is the town locksmith who resides in the same row-house block as the main protagonist, Seikichi. His public identity as a simple craftsman, however, conceals a much more complicated past and a dangerous secret life. He is a former government agent who was once a member of a specialized group of ninjas known as the Men in Black, whose primary mission is to fight aliens. Despite leaving that life behind, the events surrounding the mysterious girl Sora force him back into service, putting him in a position where he must track the very people he has come to consider his friends.

In terms of personality, Ginjiro is described as a kindly soul who does not wish to see anyone harmed, a gentle nature that constantly puts him at odds with his responsibilities to his country and his duties as an agent. He has a reputation among the other residents for being cautious and pragmatic, sometimes acting as a killjoy to the more impulsive plans of the group. His stated philosophy is that he only does what is fun, but this attitude is later revealed to be inspired by bitterness rather than true frivolity, hinting at a deep-seated cynicism born from past betrayals and trauma.

Ginjiro is a central figure in the narrative, arguably the character around whom the most complex plots revolve. He is a key player in the conflict involving the sky beasts and the government, and he is shown to be intimately connected to the story of the Silver Fox and the Night Flower, a legend referencing a past rebellion and a revolutionary named Heihachiro Oshio. Ginjiro had been recruited for this historical raid on storehouses, an event that ended in failure and suicide, and his current journey often involves confronting the scattered remnants of that part of his life.

His past is explored through his relationships with old acquaintances. He is shown to be destined by lineage to become the leader of the Men in Black, a fate he cannot easily escape. In his travels, he reunites with a former comrade from the failed revolt, a man named Tenbe Mimasaka who was left blind from their previous battles, forcing Ginjiro to confront the ghosts of his revolutionary youth when Tenbe becomes the leader of a band of thieves. Within the row house, he has notable dynamics with the young fireworks maker Seikichi, forming a kind of love triangle with the alien girl Sora, which is a source of tension and jealousy. Despite this friction, he works alongside the other quirky residents—including a mathematical genius, a carpenter, and a tile-maker—to help build the rocket that will take Sora to the moon.

Throughout the series, Ginjiro demonstrates significant personal development, primarily through the revelation of his backstory. His initial persona as a laid-back locksmith who just wants to have fun is gradually peeled back to reveal a man haunted by his violent past in the service of a government he may not trust, struggling with the weight of his lineage, and seeking redemption or perhaps just peace. He is faced with complex decisions that test his loyalties between his duty to the state and his personal desire to protect his newfound family in the row house.

Regarding notable abilities, Ginjiro is physically adept, a holdover from his days as a Man in Black. He is specifically noted for a unique skill: the ability to break any lock using only his fingers, a talent that makes him an invaluable asset to the group of builders and outlaws. He is also a capable fighter, able to engage in combat with armored men and sky beasts, and he serves as a protector for the other residents when danger arises.