TOKYO — Before Sunday, the last medal session of Olympic swimming in which Michael Phelps was not a member of Team USA was the final one in Atlanta in 1996, a realization that filled Phelps, as he settled into his commentator’s seat for NBC at Tokyo Aquatics Centre on Sunday, with a bundle of emotions he called “overwhelming.” It turns out there is no one so big the Summer Games cannot go on without them, not even the most decorated Olympian of all time.

“It’s weird. That’s the easiest way to tell you,” Phelps, 36, said in an interview between sessions of the Tokyo 2020 swim meet. “Walking to the pool this morning I was filled with tons of emotions. But for me, it was almost peaceful being here. I was so excited, just being back in [a realm] I felt so comfortable in. I’ve spent so much time in it.”

As it happened, in the first Olympic swim session since his retirement, Phelps was on hand to witness perhaps the only thing that, in terms of personal fulfillment, could have approached a 24th gold medal for Phelps himself: Team USA veteran Chase Kalisz, a Phelps protege he often compares to a little brother, winning the gold medal that had eluded him five years earlier in Rio de Janeiro in the 400-meter individual medley — and doing it in an MP Brand swimsuit, the biggest victory to date for Phelps’s swimwear imprint.

“I know how bad he wanted that. I know how hard he worked to get there,” Phelps said of Kalisz, his onetime training partner at North Baltimore Aquatic Club. “Being able to see him do it, I was in tears. I was so happy for him. [And] I’m very happy he’s in my suit. Being able to have the first medal of the swim meet won in my suit — it’s a dream come true for me. The Olympics could not have started better for me personally.”

Aside from his NBC gig, Phelps is in Tokyo as a businessman — pumping his swimwear line; doing appearances for Omega Timing, for whom he remains a spokesperson; and generally enjoying the fruits of being the “GOAT” in retirement.

The reviews of Phelps as a swimming commentator have been overwhelmingly positive, and he said he loves being able to share his accumulated insight with NBC’s viewers. Like many swimming aficionados, he said he is most looking forward to the duels in Tokyo between U.S. freestyle legend Katie Ledecky and Australian rival Ariarne Titmus in the 400 and 200 freestyle.

“This will be the first time [at an Olympics] where Katie kind of has her hands full,” Phelps said.

Since revealing several years ago his battles with depression and ADHD, Phelps peppers his answers with allusions to his mental health outreach and his continuing journey in self-discovery.

“I like being able to just be me,” said Phelps, who with wife Nicole is the parent of three boys. “I’ve been on a little journey, just understanding more about myself and why I work a certain way. I’m happy where I am. I don’t miss the training, the competitive part. I’m happy being a dad, happy being a husband.”

When he unspools himself to his full 6-foot-4 frame, he still looks as if he could throw down a sub-two-minute 200 IM, until you notice he’s a little thinner than before. The beard, too, would have to go. Since walking away from the sport for good after the 2016 Rio de Janeiro Games — at which he pushed his all-time Olympic medal haul to 28, including 23 golds — Phelps says he swims at home now only when he needs some “peace and quiet.”

“I don’t get too much peace and quiet to myself,” he said. “If I’m having one of my days, if I’m in a bad state, if I’m struggling a little bit, that’s the best place for me to go. Because it’s the most calming, the most relaxing, and I can let my mind escape. It’s almost like I’m on autopilot.”

Though he has more time on his hands in retirement, he has found that time management is an acquired skill, one he never had to learn back in the day — when his every waking hour was scripted by a coach or a trainer or an agent.

“It’s a lot harder,” he said, “because when I was competing, people told me where to go and when to go. I had to be at here for practice at this time, here for weights at that time and back to the pool for practice that time. That was basically my day. Other than that, I would sleep [and] eat. That’s all.

“Now I’m trying to wrangle three kids, trying to make sure I’m taking care of what I need to in the business world but also trying to make sure I take care of my mental health, my personal well-being. It’s a full-time job.”