Ka'ai was self-taught and since 1900 active as a musician and music educator, impressario and owner of a ukulele manufactory. He was considered the largest capacity in the field of Ukulele. In 1906, Ka'ai wrote the first textbook for the ukulele. In 1923 he performed a concert tour through East Asia and Australia and New Zealand. He then lived and worked for 7 years with his troupe in Japan.

• Ka'ai, Ernest: The Ukulele, A Hawaiian Guitar and How to Play It. Wall, Nichols 1906
• Siddall, John William (Hg.): Men of Hawaii: being a biographical reference library, complete and authentic, of the men of note and substantial achievement in the Hawaiian Islands, Bd. 1. Honolulu: Honolulu Star-Bulletin 1917, S. 157–158
• Kurokawa, Yoko: Yearning for a Distant Music: Consumption of Hawaiian Music and Dance in Japan. Dissertation. Honolulu: University of Hawai'i 2004, S. 23–26