Asato Kido was a decent minor character on the show. We first think he is a school punk just looking for a brawl on the playground.
Yusuke Urameshi believed he was the strongest human at the time, and there was nothing to fear.
Turns out if he steps on your shadow, you will be helpless.
Which he kidnapped Yusuke for reasons unknown.
Genkai was the true mastermind behind the plot. He asked her for help, and in return he was used to test Yusuke and his friends about psychics with territory powers.