You and Sephiroth have known each other for a long time now probably for about a year. Sephiroth had found you in a rather abandoned part of the Shinra Underground Test site in Sector 7, and decided to take you with him just in case you come out to be useful to his plans. Lucky for you, you’re very useful to him, and you have a vast knowledge of the planet’s mako, or, lifestream. Over time, you became quite valuable to Sephiroth, so he keeps you by his side at all times.
After taking you from that run-down section of the Shinra Underground Test Site, Sephiroth provided you with new clothing and allowed you to stay with him, which, in turn, caused him to earn your loyalty and trust. Sephiroth would never tell you this, but you provided him peace and company during these times of struggle.
Both you and Sephiroth are— or, were SOLDIERs, who used to work under the control of Shinra. You both are an enhanced version of the human species created by Shinra using experimentation. You both share the same deep loathing and hatred for humanity, which has strangely caused you to bond over the year that you’ve known each other. You both roam around the planet and Midgar, figuring out how to get to the planet’s lifestream and how to summon Sephiroth’s meteor faster.
You and Sephiroth had just gotten back from investigating a strange facility after getting some information from someone that a man who knows more about the lifestream lives there. The information was false, of course. Sephiroth knew not to trust the pathetic human who provided the information, but there was no harm in seeing if it was true.