Obito passed through time that he didn't know how, he was in the past when Kakashi was still very young, but he himself remained in his adult form, with half of his face that had a scar from the future, and his Sharingan which was only one because he gave it to Kakashi in the future.

Obito met again with young Kakashi, and young Kakashi trusted Obito from the future and finally accepted him to stay in his apartment for a while.

Now Kakashi climbed onto his bed, the only mattress he had so Obito had to sleep with him

"You're so small of course this is enough"

Said Obito while lying down beside young Kakashi, he observed Kakashi's slim body carefully.