In his business attire, Yousuke wears a black suit over a white shirt with a pink and dark red tie. He has two casual attire outfits: the first is a white T-shirt with a thin gray scarf and silver dog tag, blue jeans with a brown belt buckle, and brown sunglasses; the second is nearly identical to the first one, except he wears a red plaid shirt over the white tee and he doesn't have a gray scarf or sunglasses.
His winter gear is the same as his second casual outfit, except he sports a black winter coat over the plaid shirt. In his pajamas, he wears a thin black shirt with a pink heart over the left side of his chest and gray sweatpants with two yellow lines that wound around the hips and run down the sides.
Yousuke is a big flirt and popular with women. Due to his flirtatious personality, he comes off as irresponsible and unreliable, though he knows when to be serious when the time comes. Yousuke is also a good friend, as he will always have your back and cheer you up when you're feeling down.
Not much is known about Yousuke's past other than his first meeting with Mai (although this might be considered canon solely to the book). When Mai became lost after wandering away from her cousin and his friends, she began to cry and bumped into Yousuke. He asked her what's wrong and she began to cry after telling him "Chii-chan isn't here." Panicking to stop her from crying, Yousuke picked up Mai and lifted her up into the air. Amazed at how high up she was compared to when Chisato picked her up, Mai stopped crying. Noticing this, Yousuke lifted Mai up into the air several more times and she began to smile.
After a few lifts into the air, Yousuke asked for her name. Mai replied that she couldn't tell him her name, and when he asked why she said, "Issei onii-chan said it's good manners to say your own name before asking other people's." Impressed by her good manners, Yousuke praised her and told her his name, but before she could say hers Issei came looking for Mai. Seeing Yousuke holding Mai, Issei immediately snatched her away from him and called him a pervert. Yousuke told him he's not a pervert and the reason why he was holding her was because Mai was crying. Issei called him a liar and Yousuke replied that he's being unbelievably rude to someone he just met.
Mai interrupted their argument when she asked Yousuke to pick her up again. Issei, realizing the whole thing was a misunderstanding, apologized to Yousuke. Yousuke, however, was still upset about Issei's initial rudeness to him and pointed this out. Hearing the roughness in his voice, Mai turned silent and the two look at her when they noticed her silence. Mai began to cry, and Issei asked if she'd like him to lift her up, but Mai said that Yousuke is better than him. Issei, shocked by her rejection, weakly asked Yousuke to do so.
Afterward, Issei bowed his head down to Yousuke as he held Mai, thanking him for lifting her mood. Just as they're about to leave, Mai asked Yousuke if they'd meet again, and Yousuke replied jokingly he'd see her once she's an adult, because he's not interested in little girls. Before Issei could scold Yousuke, he held it back, afraid he'd spoil Mai's mood again.
To be added.