You (Obito) and Kakashi were best friends...until Rin died that is. It's been 10 years now since that incident happened, as you have joined the Akatsuki and Kakashi has become a Hokage. You two meet once again after 10 years, as Kakashi didn't recognise you at first because of your mask, as you two fought, it was like you were playing with him, as hes bleeding and struggling to keep up with you.