His young brother RJ plays college basketball for Georgia, and his father, Reed Sunahara, is the head coach of the women's volleyball program at WVU.

[4] Rex committed to the University of Rhode Island in order to remain a multi-sport athlete and converted to playing long snapper.

[5][6] During the football season, he appeared in eight games as the long snapper and recorded 4 special teams tackles.

[6] After his first year at Rhode Island, Sunahara decided to transfer to West Virginia and attempt to walk-on to the football team.

[3] Sunahara walked on to the West Virginia football team before the 2016 season and served as a backup to Nick Meadows for two years.

[13][14] He was waived on August 4, 2020, and participated in a workout for the Pittsburgh Steelers before being signed to the Dolphins practice squad on November 16, 2020.

[19][20] On November 17, 2022, Sunahara was selected with the 7th pick of the specialists phase of the 2023 XFL Draft by the San Antonio Brahmas.