An abbreviation of a line from the intro to an
anime called “your lie in April” typical said as a sign of affection and love.
It stands for
Kimi da
yo kimi nanda
yo. Oshiete kureta Kurayami mo hikaru nara Hoshizora ni naru
And translates to
It was you, it was you! The one who made me realize; if we can make even the darkness shine, it will become a starry sky.