Like all people, Marui had, once sometime long ago, parents to depend on. In his memory, they might as well have disappeared. Marui grew up by himself, taught himself, supported himself…everything he knew came from research that he did – that, and intuition. His memories before meeting Fuyuki, Suzume, and Asakura-san were of people praising his smile and grace that made him appear more mature than he was. He knew that those people could not find anything else to say to a kid living alone…so he practiced his charm until people would no longer question his living situation but rather see him as an adult.

Growing up alone had impacts on Marui's character more than just his maturity though. He grew to understand the art of subtle manipulation – changing his expressions just enough to have people do what he needed, outright provocation, and sword and fan fighting (he could not, in good reason, purchase a gun at such a young age) in order to survive. The good thing was, his manner of acting and speaking made sure he never had any enemies on the streets.

At age 7, Marui had met and got along well with Fuyuki and Suzume, but never revealed that he was living by himself. They became a family that he needed, but Marui – true to his nature – treated them as little sisters and refused to depend on them. When Marui first met Asakura-san, he thought she would not ask about his living situation either. Eventually, though, she discovered that he was by himself and forcefully began including Marui in all their family activities, trying to make Marui less self-dependent. Eventually, though Asakura-san was murdered and Marui was not there to stop it from happening. He happened upon the aftermath of two crying sister-figures, and the haunting knowledge that people he cared about could die so easily made him vow to live his life out by enjoying the moment.

By 15, Marui had 'earned' enough money to purchase a flat in town as well as a new wardrobe. When he was small, he had no choice but to meticulously pick every piece of clothing that he wore so he would appear well-dressed, and this habit carried with him in his purchase of a new wardrobe – clean-cut black clothing dominated his closet. He found that his grace that he cultivated from the streets worked well with traditional Japanese clothing, and therefore enjoys wearing those. He also chanced upon a pair of daggers and some needles when shopping in town for supplies for his new flat, because his fighting nature never left despite him having enough money to live comfortably for a while. He realized the needles could be hidden into the spokes of his fans and the daggers under his jackets.

All this time, he still kept in touch with his childhood friends Suzume and Fuyuki, but couldn't help but blame himself for not being there to stop the murder from happening. He was never able to come up with a good answer when the girls asked why Asakura-san had to die, so he slowly fell out of touch with the two. He still celebrated their birthdays and holidays together, but did not move into Fuyuki's mansion when they decided to create a Famiglia, until he was called by Suzume to help with her mission.