Killua sits next to 3 phonetic neighbors — Silas, Killian, and Kaito are the closest matches by sound. Most share Killua's Japanese cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"fictional invented name, no established meaning"
"he who descends"
"people's power"
"invented creative variant"
"poet, deep one (via Devon)"
"beloved"
"that which is believed"
"thankful warrior"
"belonging to God"
"my God is the Lord (Yahweh)"
"twins"
"supreme ruler, monarch"
"modern invented name"
"spear land"
"watchful, alert, awake"
"settlement of the prince, princely estate"
"true, faithful, trustworthy"
"oak grove, oak tree"
"slender, narrow"
"royal court attendant"
"split, torn, broken apart"
Similar sound: These names share phonetic patterns with Killua — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Japanese (fictional) origins, giving them the same cultural heritage as Killua.
Rhythm: Killua is a 3-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.