Tyus Jones was Tom Izzo’s Plan A, Tyler Ulis his Plan B.

Tum Tum Nairn, well, he turned into Plan C when Izzo needed a point guard in his 2014 recruiting class.

There was room for Gavin Schilling in 2013 when Jabari Parker spurned Michigan State for Duke.

Izzo signed Ben Carter as a grad transfer in 2016 because Deyonta Davis surprised him by leaving for the NBA.

MSU’s senior class was anything but MSU’s first choice.

There are no regrets.

This small, unheralded 2018 senior class — which plays its final game at Breslin Center Tuesday night against Illinois — has turned into an important group in a program that has survived the reasons they were recruited and thrived with them in the fold.

Nairn and Schilling have bridged multiple eras while being critical to the success of both of them. They started for MSU in the Final Four three years ago. They should finish with at least a Big Ten title, the program’s first in six years, a share of which the Spartans can clinch against the Illini.

That’s not the case if Schilling doesn’t perform as he did against Purdue just 10 days ago — as MSU’s best option for a solo defense against Isaac Haas.

A lot of things aren’t the case if Nairn isn’t part of the program. And, no, not for the better. You might not recognize MSU’s team today if Nairn had never arrived.

Nairn’s impact on MSU’s program is hard to see sometimes when he’s on the court. The severity of his offensive limitations are magnified when he’s in the game instead of Cassius Winston. It’s better for Nairn — and the perception of him — when he and Winston are on the court together or, in years past, when he was on the court with Denzel Valentine.

Nairn’s effect on the program is deeper than being the spark in the starting lineup that helped save MSU’s season before its improbable Final Four run three years ago. It’s more profound propelling MSU past Minnesota a year ago in Minneapolis. Without that win, I don’t think MSU is in the NCAA tournament field.

In terms of creating offense, MSU would have been better off with Jones in 2014-15 or Ulis for several seasons.

But culturally, the program wouldn’t have been as strong. Izzo wouldn’t have been as happy. He’d probably still be around. Probably. Though these last few seasons, he’ll tell you, have been reinvigorating. At least one of Izzo’s staffers, assistant video coordinator and resident sounding board Doug Herner, said he would have retired a couple years ago if Nairn hadn’t arrived.

“I can’t leave Tum,” Herner said then.

“I’d be lying if I said I knew I’d be able to inspire people the way I have since I’ve been at Michigan State,” Nairn said Monday. “To hear people talk about me the way they do, it makes me think about my mom a lot and my dad a lot and just where I came from. And to know, my mom always told me, ‘Manners and respect will take you further than any sport will take you,’ and (that) I stuck with what I learned when I was growing up as a kid.”

There is irony in the culture of MSU’s basketball program being under attack. Anyone who’s been associated with the program for a long period of time will tell you the culture has never been as healthy as in recent years, never before has the program been filled with so many good kids.

Nairn is a massive part of that. He’s what separates now from other good eras.

“He’s special,” MSU assistant coach Mike Garland said before the season. “In terms of kid and character and person, he’s got to be the ultimate guy in terms of that. There’s nobody who’s been here like that.”

Izzo knows life will be more difficult once Nairn leaves.

“I said to my (coaches), ‘You’d better start working harder, because (in) one meeting we had (I said), ‘Did you call everybody (all the players)?’” Izzo said Tuesday, re-telling a story he’s told before. “One of my assistants said, ‘No, we just call Tum and it gets handled.’ I said, ‘You’re lucky, because that’s not how it is all the time.’”

Nairn has played a valuable role in recruiting present and future players. And he is, perhaps, part of the reason Miles Bridges stayed, Izzo surmises.

“He had a close-nit group there,” Izzo said of Bridges, “but Tum was the Pied Piper. … (He) definitely had a serious impact.”

No player I’ve been around frustrates fans like Nairn. No player I’ve been around loves his teammates, coaches and community more than Nairn. No one I’ve covered has brought more vitality to a program off the court.

“He has a different aspect on life,” Schilling said of Nairn, who comes from humble beginnings in the Bahamas. “To have somebody around you like that every day is really uplifting.”

Nairn loves MSU so much he’s visualized kissing the Breslin Center court tonight. “I didn’t practice it,” he insisted, laughing. “I envisioned myself doing it.”

He should be beloved by MSU fans. If only he had a willing and capable jump shot or a better knack for offense.

His legacy will be complicated. In time, you’ll appreciate him more for this:

“I just really hope that people know that I’m a man of faith and I’ve always lived my life that way. Just that I give everything to the program that I have.

“I never took a day off. I never took a practice off. Never skipped a lift. Never took a sprint off. Anything that had to do with this program, I did it with all my heart and I meant it from the bottom of my heart.”

Contact Graham Couch at gcouch@lsj.com. Follow him on Twitter @Graham_Couch.