Early Life

Yatsu is the oldest child of a maths professor and a biologist working in research.
His parents met at a conference, where they immediately hit if off and started a relationship because they felt it was the natural way to go. Their first child was Takuyatsu, who was meant to be the leader of his siblings, socially and academically. His parents always wished for him to become successful and respected, helping them with their other children and setting a good example for others around him - unfortunately for them, he turned out to be an absolute flake academically.
Yatsu had a lot of trouble with focusing in class and studying, especially when it came to maths. He did well enough in subjects like art and music and was very popular in his class even at a young age, but that wasn't what his parents were looking for.
A psychologist couldn't help him and urged him to just try harder - maybe he would grow out of it.

Growing up

Well - he didn't grow out of it.
In secondary school, Yatsu's social skills really seemed to shine. He took on the role of a leader during school - not the stern, responsiblekind but the caring, fun-loving kind and there wasn't a single kid in his class that was excluded for being shy or quiet. Somehow, Yatsu could make everyone feel welcome.
If he got into trouble, it would be for getting into fights with bullies or mean older kids - which were fights he never started - not showing up to class or disrespecting authority, something that usually happened if 'autority' didn't respect someone else. At home, his younger sister Fuyuko turned out to be very academically capable and outclassed her older brother in most subjects, despite being a year younger than him. They even take some classes together because she is just that much ahead - something that annoys Yatsu every time it happens.

But Fuyuko wasn't the only one of his siblings expressing these kinds of traits - his younger twin brothers Haruto and Daiki were making it clear from a very early age that they both had a gift for sciences, specifically chemistry and biology, making their mother in particular very happy. The only one of his siblings not one-upping Yatsu every step of the way and therefore the one he has the best relationship with is his youngest sister Akiko. He spends a lot of time taking care of her or playing with her and he is easily her favorite sibling - not that much of a title, considering the twins can get rather menacing and enjoy picking on their little sister quite a lot, something that frequently causes fights among the three brothers.

To be continued...

Now that Yatsu has reached eleventh grade, his demeanor has changed a little bit.
He's settled down a little and isn't trying as hard anymore to be positive and cheerful, as he's given up a little on making his parents happy, now that they've got so many 'better' children to take care of that.
He's still very poular, but leaves most of the stupid pranks and partying to his best friend Noboru. However, that doesn't stop him from enjoying his status, especially since the last few years really contributed to his reputation among girls. He's popularity with them stems from his expressed confidence, his soft hair that feels like you're touching an actual cloud, his good looks and fashionable clothing and his natural charme that makes him always know the right thing to say.
His favorite subject is sports, where he is one of the fastest runners and Spanish as well as English, stemming from his talent when it comes to languages. He's recently been fooling around with girls at the school on Sundays after word got around that the caretaker never locked a particular door, allowing students to sneak into the building.