At 6-foot-9, 270 pounds, he is one big baby _ and he has made some sizeable contributions to Duke's run to the national championship against Wisconsin on Monday night without even playing in a game.
Obi is a rare transfer into coach Mike Krzyzewski's program and can't play this season due to NCAA rules. He can practice so he gets to go up against star freshman Jahlil Okafor when the Blue Devils scrimmage.
"He tells me, 'Sean I need you to, if you can hurt me, hurt me. Play me really hard,'" Obi said Sunday. "We do stuff with the coaches after practice. I give him that test every day in practice. He's definitely benefitted from it. And I have benefitted from it, too."
Obi has come a long way in a short time, both on the court and off.
He grew up in Kanduna, Nigeria, playing soccer, loving and playing soccer. At 15, and 6-7, he decided to give basketball a try with some prodding from friends and a local coach.
"I just picked it up really fast," he said.
With his family's blessing, Obi decided to use basketball as a path to an education in the United States and possible scholarship. His uncle knew a man named Steve Eggers, who worked in the oil industry and often traveled to Nigeria for business, and asked Eggers for help finding Obi a family to live with in the U.S.
"Guy comes up to him and says 'I have the next LeBron James,'" said Hunter Eggers, Steve's son. "My dad sort of rolls his eyes. 'They're all the next LeBron James.' He said, 'No, no, no, you really have to see this kid.'"
Steve Eggers met Obi's family and decided to help. Hunter Eggers, six months older than Obi and with two older sisters, took it a step further.
"I kind of just looked up and said, 'Why can't he live here?' Hunter Eggers said. "Took my parents aback a little, but they liked the idea."
And that was that.
"From the first day he was part of our family," Eggers said. "There was never a transition."
Eggers and Obi played on the same basketball team in Greenwich, Connecticut, at small high school that didn't draw much attention from scouts.
Obi progressed fast. He arrived weighing 180 pounds and in a couple years had put on about 60 more.
Still, Obi was off the radar and lightly recruited. He and Eggers went to Rice in Houston, where Obi was one of Conference USA's top freshman last season. He averaged 11.4 points and 9.3 rebounds. A coaching change prompted he and his brother to transfer.
Obi's second recruitment drew the big names such as Duke, Virginia and Michigan.
"Visted Duke. Fell in love with it. Fell in love with coach," Obi said.
Obi is just the fifth player to transfer into Duke in Krzyzweski's 35 seasons. He said sitting out has allowed him to work on his game and get ahead on his class work. He is double-majoring in sociology and markets and management.
"It's hard to sit on the bench and watch all the time, but hopefully it'll pay off in a better way," he said.