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LSU head coach Paul Mainieri stands in the dugout during Game 13 of the College World Series between LSU and Oregon State, Saturday, June 24, 2017, at TD Ameritrade Park in Omaha, Ne. LSU eliminated Oregon State 6-1, putting the Tigers in the College World Series Finals.

LSU coach Paul Mainieri had an unwanted companion every day for the past three months or so, and he’s not sure if its presence will ever leave his side.

It’s the memory of the final days of last season — two consecutive losses in the College World Series championship round. Those two games will forever taint Mainieri’s memory of what was, in most respects, a great season.

It’s hard to be satisfied in this business, Mainieri said.

“It’s been gnawing at me all summer, ever since,” Mainieri said. “It’ll probably gnaw at me until I’m put in my grave. That’s the way it is.”

While that memory is still fresh, his team will take its first step toward moving forward Sunday when it goes through the first of 27 full-squad fall practices.

The team that plays on the Alex Box Stadium grass Sunday will look markedly different from the team that watched Florida celebrate a national championship at TD Ameritrade Park in Omaha, Nebraska.

Half the starting lineup and two-thirds of the weekend rotation are in professional baseball. The other piece of the weekend rotation, Eric Walker, will miss the 2018 season as he recovers from Tommy John surgery.

Of the 35 players on LSU’s roster, 18 were not on the team last spring.

It’s a similar situation to the one Mainieri found himself in before the 2016 season started, when he only returned one starter in the everyday lineup from a team that went to the College World Series.

That team went 45-21, including a 19-11 record in the Southeastern Conference, and finished the season two wins short of Omaha.

The difference between the 2016 team and this team, Mainieri said, is that he has to replace much of his pitching staff.

“In order for us to be competitive for the championships that we want to win, we’re going to have to develop that pitching staff first and foremost,” Mainieri said.

The cupboard is certainly not bare. LSU returns Zack Hess, who developed into a star during the Tigers' stretch run, as well as Caleb Gilbert, who went 5-0 with a 0.68 ERA over his final nine appearances last year.

But even those two do not have clearly defined roles as the Tigers enter fall practice, and the pitching staff beyond them is full of unknowns. It’s a top priority for Mainieri to have pitchers' roles start to come into focus this fall.

Before he sees them pitch in a competitive situation — LSU will have scrimmages on tap for nearly every day of the fall schedule — Mainieri said “we’re not even close to getting those questions answered.”

The outlook for the LSU lineup is clearer, with established players like Antoine Duplantis, Josh Smith and Zach Watson returning.

But after losing Kramer Robertson (.307, 43 RBIs), Cole Freeman (.315, 19 stolen bases), Greg Deichmann (.308, 19 HRs) and Michael Papierski (.256, 11 HRs), the Tigers still have much to figure out there, too.

Sunday will be the Tigers' first day to see all the new faces together in competitive situations. The mission is the same as it is every fall, Mainieri said — but it takes on added importance with new players.

First, he wants his team to get an understanding of what he means by playing “the LSU way.”

“It’s not something special or different or reinventing the game,” Mainieri said. “It’s just that our way is that we want our players to play hard but smart, fundamentally sound. ...

“You want to teach them the fundamentals and our style of play, so to speak — a hustling, confident, attacking style.”

Second, Mainieri wants to create a competitive atmosphere to get a clearer picture of which players he will lean on next season. That will be accomplished with scrimmages in 26 of the 27 scheduled days of fall practice.

“The questions won’t be answered with 100 percent certainty at the end of fall, because it’s a fluid thing as you’re going into the season,” Mainieri said. “But at least after 27 days of practice, you get a better idea.”

Follow Luke Johnson on Twitter, @ByLukeJohnson.