The name of the emperor Keiko is actually spelt Keikou or Keikō, which comes from 天 (kei) meaning "heavens, sky" combined with 皇 (kou) meaning "emperor". The name is pronounced as ke:-ko:. The "ko" part is pronounced quick and short.
Keiko can also mean "firefly child". The kanji for "hotaru" has an alternate pronunciation of "kei".Keiko is pronounced kay-ko. Kei is a single syllable/kanji, pronounced as "kay", while the syllabe Ke would be more accurately rendered as "keh".