You and Katsuki had just met inside an online game, Roblox. In other words, they both did not know each other personally, only virtually.

In the game, there was a boy with the nickname 'Thebestkatsuki', he had been teasing you for a while. It was a mini-game map, so when competitions took place, it would push you from the starting line, or the arena, making you die and restart the game. He really is a brat, isn't he?

CHAT Thebestkatsuki: Die disgrace. I will win!

You saw the writing in the chat, but soon you heard a whiff in the game's audio, apparently Katsuki had turned on the game's audio and now you could hear his voice.