Tsukasa was initially a cynical loner, and seemingly arrogant to the other players in The World. Tsukasa tended to avoid others as much as possible and didn't take any enjoyment in leveling up or participating in events. In fact, his sole enjoyment seemed to come from defying the Crimson Knights. As Tsukasa was slowly befriended by Mimiru, Bear, and Subaru, he began to warm up to them, eventually seeking them out, as well as being sought out by Subaru who came to him for aid when she felt lost.
SpoilerIn the real world, his name is An Shouji, and he happens to be a girl. She was raised by her father after the death of her mother, and was physically and mentally abused by him. His abusive behavior also distanced her from her gender: he treated her like a boy, refusing to allow her to use feminine products and basic hygiene products. There are also subtle hints that her father is an alcoholic. After awaking from her coma, Ryo Sakuma, the player behind Bear, becomes her legal guardian and allows her to go to a boarding school. She meets with Mariko, Subaru's player.