2000s

The Cleveland Indians signed Tadano as a free agent in 2003, and he rose through the Cleveland farm system, making his debut in 2004. He made 14 appearances and four starts with a 4.65 ERA in 50⅓ innings. In January 2004, it was widely reported in America that Tadano was featured in a gay porn video A Midsummer Night's Lewd Dream (真夏の夜の淫夢, Manatsu No Yo No Inmu), three years previously, with Tadano appearing at a press conference organized by the team.^[2] Tadano said, "I was young, playing baseball, and going to college and my teammates and I needed money."^[3][4]

He was sidelined due to an injury early in the 2005 season, but recovered and was shuttled between Cleveland and the Buffalo Bisons for the rest of the year.

On April 4, 2006, Tadano was traded to the Oakland Athletics for outfielder Ramon Alvarado.

In 2007, Tadano was sent down to Oakland's Double-A team, Midland, after being invited to spring training. He was eventually promoted back up to Triple-A and started off well, looking sharp with a plus splitter. Curiously, he ran into trouble in June. His ERA ballooned as he gave up 29 runs over 5 games. He was moved to the bullpen in July after Oakland demoted Colby Lewis and Shane Komine.

In 2007, he was the 1st pick by the Nippon Ham Fighters in the university/company player draft. He would become one of the last players of the Matsuzaka Generation to start his NPB career. He missed the start of the 2008 season with an injury.

2010s

In 2012, he played in his first Nippon Series against the Yomiuri Giants. However, he was thrown out of the game because he was judged to have thrown a bean ball at Ken Katoh, the Giants' catcher. He is the first pitcher to be thrown out of the game for a dangerous pitch in Nippon Series, though his pitch did not hit Katoh.^[5]