The Secretary General of the Rwandan club, Bernard King Itangishaka confirmed moves to sign Ulimwengu, a player Rayon Sports had been monitoring for a long time.
The 19-year-old Burundian striker was until recently playing for Sunrise FC, another top flight side based in Eastern Rwanda.
The striker will Join Rayon Sports from Sunrise FC for a club-record fee of 8 million Rwandan francs (about $9,000).
The recruitment of Burundian striker by the Rwandan club comes two years after his compatriot defensive midfielder Gael Duhayindavyi signed a two-year deal with Rwandan first division side Mukura Victory Sports.
Duhayindavyi, 28, is captain of the Burundian national football team.