to summarize, kakashi got his sharingan eye from his friend who
is from the Uchiha family. he died from a mishap during a
mission.
very touching story. remember how kakashi fail naruto, sasuke and
sukaru in book 1 because they fail to work as a team and only
follow rules? in the side story kakashi used to be one who only
know how to follow rules and learnt a valuable lesson about the
importance of teamwork.
read the manga for more info. chapter 239 to 244.
