From a young age, Shohei Ohtani was exposed to various sports, but baseball stood out above all else as the one he loved most.
He has also said that growing up in Iwate played an important role, as it allowed him to encounter baseball in an environment where he could truly enjoy it and continue loving the game.

Within that setting, Ohtani began to display exceptional talent early on — both as a pitcher and as a hitter.
Looking back, he says,
“Ever since I was a kid, I’ve always wanted to do both. I wanted to be a good hitter, and I wanted to be a good pitcher.”

Turning professional was simply a continuation of that desire.
After joining the Hokkaido Nippon-Ham Fighters, Ohtani set his sights on pursuing a two-way path. When asked why he chose to do both, he explained that it was not about proving that a pitcher could hit or that a hitter could pitch.

“I wasn’t trying to show that I could do both,” he said. “I just wanted to do both.”

Even when told that he might become a better pitcher by focusing on pitching alone, Ohtani replied,
“All I can say is that I really want to be a good hitter as well.”

For Ohtani, being a two-way player was not a strategy or a statement.
It was simply the natural continuation of the baseball he had always wanted to play.

Source

This quote comes from a Japanese book published in Japan and is not currently available in English.

The Path to Shohei Ohtani, the Two-Way Major Leaguer, p.31