Letizia Alto and Kenji Asakura started buying rental properties in 2015 to free themselves from 80-hour workweeks.

The physician couple, who met while working at the same hospital, were essentially starting from scratch. Asakura had dipped his toe into real estate investing in the early 2000s — he was mostly buying and reselling land — and lost money during the 2008 housing market crash, while Alto had never owned property.

Their first investments were two duplexes, which they purchased with money they'd earmarked to buy a primary residence. They wouldn't buy a primary home until 2022, but in the interim, they continued expanding their rental portfolio. As of 2025, they own more than 100 units.

The rental income has allowed them to step back from the hospital, spend more time with each other and their kids, and build their online community, Semi-Retired MD.

"We were self-taught," Asakura told Business Insider.

Alto added, "We were reading all the time."

The couple, who live in Puerto Rico for about half of the year and spend the other half traveling, shared the three books that helped them scale their real estate business.

The couple read Robert Kiyosaki's personal finance classic, which is particularly popular within the real estate investor community, before buying their first property together. They were on their honeymoon, traveling in a camper van through New Zealand. Without electricity, they passed the nights reading "Rich Dad Poor Dad," and some of the author's core themes resonated.

"It was really powerful. We were like: 'Oh, my gosh, this is it: We're employees, we trade our time for money, we're never going to be able to be in Italy for three months at a time because we're always going to have to be working,'" said Alto, whose dream was to spend more time traveling. "The only way it works is if we have another source of income, outside medicine, that can replace part of our salaries so that we can have the freedom to take time off."

Shortly after returning from New Zealand, with Kiyosaki's lessons on their mind, they bought their first two duplexes.

Books like Garrett Sutton's about LLCs have helped them expand their business knowledge, which has been key to their success.

"I think a big differentiator is that we apply a lot of business principles to our rental business," said Asakura. "A lot of people don't think about rental properties as a business — they think about it as providing housing — but ultimately, each property is a mini-business."

"The Millionaire Real Estate Investor" by Gary Keller

Gary Keller's book explores real estate investing strategies and practical, actionable advice. The couple said they built their cash-on-cash calculator, which helps them ensure a property will generate positive cash flow before closing, based on the one provided in Keller's book.

It also gave them the confidence that they could succeed in the real estate investing world. The author incorporates interviews with more than 100 millionaire real estate investors with all sorts of backgrounds.

"We could see that people just like us could do it," said Alto, adding that confidence is just as important as executing your investment strategy. "If you don't believe it's possible, then you're always going to look for the reasons it's not going to work, and you're going to be stuck in analysis paralysis for the rest of your life."