The 19 year-old defender signed for City today from Palmeiras.
Asked why he chose City, Reis told the club's website: "The magnitude of Manchester City, its history and its structure.
“I followed a lot in the last few years. All we watch on TV is Manchester City so every kid that loves football is certainly watching Manchester City.
“When the door knocked and it was Manchester City, I knew there wasn’t anywhere else to go.
“I believe it will be the biggest challenge of my life but any player who wishes to play in elite football has to come here and play football here.
“This is a dream come true. Since I was a young kid I’ve always dreamt of an opportunity just like this one and to play for a Club as big as City.
“This achievement isn’t just my own but also my family’s too and everyone that has helped me get here.
“It is an amazing achievement and I’ll work very hard to make it a very happy one.”
Reis also stated: “Here I believe that your goals must be as high as possible, because is a club that always reaches high level.
“But for now I want to fit in my place, with my humbleness, do my work, find my space, win titles, Champions League and the titles we compete for.”