INDIANAPOLIS >> DeForest Buckner is preparing for Sunday’s game the same way he does every week.

The Indianapolis Colts’ star defensive tackle studies tape, focuses on executing the game plan, making sure he’s in top shape and doing everything he can to help his teammates make it back into the playoff hunt.

Still, he admits this one feels different.

Buckner spent his first four pro seasons with the 49ers, then was traded in the prime of his career to Indy, a move that forced him to leave his heart in San Francisco as he moved on with his career. On Sunday, he’s going back for the first time.

“Definitely don’t know how I’m going to feel when I get out there on the field,” he said Wednesday. “I’ll probably have a mix of emotions. That’s where I started my family. That’s where I got to start playing this game at the highest level. I poured my heart and soul into it for four years there, so it’s going to be interesting.”

The trade was a surprise in NFL circles.

Teams typically covet Pro Bowl-caliber defensive linemen in their 20s, especially interior linemen who are as disruptive as Buckner. But facing the possibility of losing Buckner in free agency, a salary-cap situation that would have made it challenging for the 49ers to keep the 6-foot-7, 295-pound Punahou alum from Maili, and a depth chart full of talent, San Francisco sent Buckner to Indy for a first-round draft pick in 2020.

Colts general manager Chris Ballard wasted no time handing Buckner a four-year contract worth $84 million — a price the 49ers couldn’t afford — and instantly making him the anchor of Indy’s defensive line.

“It doesn’t really happen but it’s the nature of the business,” Buckner said, referring to the trade. “It’s what we signed up for, right?”

Buckner certainly has held up his end of the deal. He’s one of three NFL defensive tackles with seven or more sacks each of the past three seasons. He has a league-high 348 tackles among interior linemen since entering the league in 2016. Last season, he earned All-Pro honors for the first time despite playing most of the season with essentially one arm.

This season, a healthy Buckner made no secret he expected to play even better —- perhaps well enough to be selected the league’s Defensive Player of the Year.

Statistically, Buckner again ranks among the league’s best. He’s fifth among defensive tackles with 28 stops and has two sacks.

Yet to achieve his goal, Buckner knows it will take better performances from himself and his teammates.

“It doesn’t just take one guy, it takes the whole unit, and as a unit we can definitely rush the passer a lot better,” he said. “You know you just give up those opportunities where on third down you could have gotten off the field, a couple guys had great rushes but we just couldn’t contain him.”“

And as he studies game tapes this week, Buckner acknowledges it is a little odd to be strategizing against former teammates such as quarterback Jimmy Garoppolo and right guard Laken Tomlinson. They were there for what wound up as Buckner’s final game with San Francisco — a 31-20 Super Bowl loss to Kansas City.

A few weeks later, Buckner joined the Colts. Buckner acknowledges he’s watched the Super Bowl multiple times, thinking of what could have been.

But as reunion weekend approaches, Buckner wants to take care of business against his former team while enjoying the brief time he’ll have to meet some old friends.

“It’s a little personal if you want to say that,” Buckner said, chuckling. “It’s been a little quiet this week. They’ve got a game to focus on and I’ve got a game to focus on, so I’ll see them on game day and then maybe catch up with them after the game.”