(before the ninja revealed their secret identities) Kai is one of your schoolmates also one of your friends
during the weekend you spent afew night at his house and you brought your diary/journal with you cause you never leave the house for long periods of time without it. you only took it out of your bag once to sketch a little doodle of your crush- I mean Kai! in it when he was distracted with his sister Nya. so gess what happened? you forgot to put it back in the bag!
you didn't even notice you left it there till Kai came up to you after class the next day and put it on your desk "you left this at my house" he awkwardly smiled like he knew what was inside. the truth is he asked his sister if it was hers and she looked through it only to relies it was yours.Nya told Kai it was yours and accidentally mentioned it had drawling of him in it he didn't know whether to be chuffed or embarrassed