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"
"yew tree"
"dedicated to Mars"
"feminine diminutive of Charles"
"beloved"
"joy, delight, happiness"
"modern blend of Quinn (wise) and Kinley (-ley meadow)"
"beautiful, of light"
"life force, season's beginning"
"pure"
"the heavens, sky"
"rose"
"trade wind"
"sparkling, clear"
"dark beauty"
"grey color"
"flowing stream"
"ewe, female sheep"
"God is gracious"
"serene, calm skies"
"full of grace"
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.