A blunt and brilliant specialist in astrolinguistics and related fields who joins the USS Discovery in 3190 as part of the delegation sent beyond the galactic barrier to make first contact with Species 10-C.
Doctor Hirai appears in the closing run of the fourth season, including The Galactic Barrier, Rosetta, Species Ten-C and Coming Home, played by Hiro Kanagawa. He comes aboard with President Rillak, President T'Rina and General Ndoye.
Hirai has little patience for small talk and says exactly what he thinks, which irritates some of the crew, but his expertise is real. He helps to work out that the 10-C communicate through hydrocarbons carrying emotional meaning combined with patterns of light.
Working with Burnham, Saru, Stamets and Zora, he contributes to the mathematical bridge language that finally lets the two sides understand one another.