His father, Paul Daniel, is an American, and his mother, Yasue, Japanese. He grew up in various places in the world. He spent most of his elementary school days in Nagoya, Japan. He went to the Nagoya International School. He and his family moved to Spain when he was fourteen. He speaks English, Japanese, and Spanish. He has one sister, Kana.
Taro started playing tennis when he was 7, He practiced at the Shinrin Longwood Tennis Club in Nagoya City during his years in Japan. He got third place for under 12 in the All Japan Junior Tennis Tournament.
Qualifying for his first ATP tournament, he made the quarterfinals of the 2014 Royal Guard Open in Viña del Mar, after gaining revenge over Bellucci and defeating eighth seed Federico Delbonis. Previously, he had won a couple of Futures events and made the semifinals or finals of some Challenger Circuit events.