Simmons missed all of last season with physical and mental health issues after being traded from the Philadelphia 76ers.
That game will bring an end to a tumultuous off-season for the high-profile club, the unvaccinated Irving back after missing a bulk of last season and Durant also requesting a trade that didn't eventuate.
"It's not too often you get a chance to see a 6'10 guy do the things he does," Melbourne-born Irving said of Simmons. "What I've been able to observe ... is his resolve and resilience ... whatever greatness looks like for him, he wants it.
"When you're in an environment where you can be supported, that can help ease the journey.
"That's a role I'd like to play on this team ... protect him when needed but know he's a big boy, he can handle it."
Mills told reporters he had asked Simmons if he was ready to play one-on-one, to which Simmons replied, "I'm ready to play one-on-five".
"Rome was never built in a day ... the ability for us to create this bond between us with the adversity that comes hopefully can tie us stronger together," Mills said of the franchise's dramatic last 12 months.
He said Simmons had learnt from "the good, bad and ugly" of his career.
"I've supported him from afar for a long time now," he said. "To step on the hardwood with him, I'm really looking forward to it."
Simmons insists he's mentally prepared to return to the NBA.
"Everyone has dark days; when you're able to address it and work towards a place you need to be, that's where I am," he said. "I don't care about narrative, or people saying certain things.
"I'm going to go out there play, I'll let everyone else talk ... expectations, that's for you guys (in the media)."
"I'll try and be as annoying as possible," he said of his trademark defensive niggle. "There's been some ups and downs for sure, probably downs that I'd never thought I'd go through, but it's a part of the process.
"Hopefully my injuries are behind me now and I can go ahead and help this team."