Koi sits next to 5 phonetic neighbors — Joy, Coy, and Roy are the closest matches by sound. Most share Koi's Japanese cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"carp fish; symbol of perseverance and good luck"
"bright, shining one"
"hill, hillfort"
"stone worker"
"orange tree"
"fine red cloth, luxury textile"
"magical, illusory beauty"
"divine energy, yah-blessed"
"royal meadow, king's clearing"
"beautiful, radiant as a dove"
"heavenly calm, noble tranquility"
"God will add, God increases"
"pure"
"beloved, wished-for child"
"variant of Kinsley"
"from Britain, a Briton"
"possibly bright one, cheerful"
"ruler of the land"
"heavenly calm"
"little fire, descendant of the fiery one"
"winding valley"
Similar sound: These names share phonetic patterns with Koi — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Japanese origins, giving them the same cultural heritage as Koi.
Rhythm: Koi is a 1-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.