Niwa had a prolific junior career that began on 2008. He reached the quarter-finals at the 2008 India Junior Open in Pune, India, and won the doubles title with his partner, Yuki Hirano. At the 2008 World Junior Champions… See more

Niwa and Kenta Matsudaira were doubles partners from 2008 to 2015. Their playstyle is characterized by both players' unorthodox playstyles, with Niwa frequently incorporating "chiquita" banana flicks and Matsudair… See more

Niwa and Chen have met 9 times in the international scene, with Niwa leading 5–4. Their first encounter was at the 2009 Harmony China Open where Niwa won 4 games to 1. They met another two times at the 2011 H… See more