He was born with golden hair and sharp honey coloured eyes. Those were the only things that set him apart, and made him any kind of special. In the kingdom of Karasuno, those who were born with such features had to be treated with great deference, since they were destined for greatness. They bore the sign of the Gods, and commonly called Seares.
Tsukishima Kei was a Seare but honestly, he didn't feel that he was meant to be one. All he wanted was to live a simple life, but Seares received royal treatment. Tsukishima was incredibly lonely, often ignored by his peers, but it all came to an end when he escaped to Nekoma.
Nekoma was a safe haven for everyone, a small town in the outskirts of Karasuno; housing with no discrimination all species. The Chleon people were such a species, and they were the opposites of Seares with black hair and dark eyes, supposed marks of the underworld. Outside of Nekoma, Chleons were treated as vermin, but there they could live a peaceful life.
Kuroo Tetsurou was a Chleon wizard who wanted greatness and lived a hollow life constantly hiding every thought. Living in Nekoma was boring, uninteresting, a place with no aspirations.
Tsukishima was the first Seare to gain access to Nekoma; he wandered the streets for days until Kuroo took him in. At first it was out of sheer curiosity and boredom but then the two of them fell in love with each other against all odds. Kuroo and Tsukishima found their happiness together.