Before joining Rayon Sports, the 20-years-ol Burundian striker was playing for his home-side club of Olympic Star, where he was the Burundian league's top scorer in last season with 12 goals.
In a statement, the club said that Nihoreho inked a deal until the end of the 2021-2022 season.
Earlier Monday, another Burundian coach Jean Marie Vianney Ismail Nduwantare has been appointed as new manager of Rwanda's first division club of AS Muhanga (South)
Before joining Muhanga, Nduwantare was coach of Gicumbi FC, another first division club in Northern Rwanda, where he was fired after a poor run of results in the country's top flight.
Rayon Sports finished as 2018/2019 Azam Rwanda Premier League champions with 72 points followed by APR with 65 points.
In May this year, Army side APR FC were crowned Rwanda Premier League champions for a record 18th time after the Rwandese Football federation (FERWAFA) called an end to the season due to the COVID-19 pandemic.