Koi sits next to 3 phonetic neighbors — Kai, 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
"love, romantic feeling"
"modern phonetic creation"
"American invented name with theophoric -jah suffix"
"the kingdom of Ciar, County Kerry"
"Dack's settlement"
"wood, forest"
"peace"
"growth, abundance (Arabic root interpretation)"
"star"
"wisdom and fire (fictional Fire Nation general)"
"winner, victorious fighter"
"Carl's town or farm"
"hazel tree"
"earthworker (as short for George)"
"belonging to Christ"
"the Lord is my God"
"the color blue, sky and sea"
"Yahweh is gracious"
"resolute protector"
"father holds"
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.