Arcaius sits next to 3 phonetic neighbors — Arcadius, Lucius, and Cassius are the closest matches by sound. Most share Arcaius's Greek-origin cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"from Arcadia, of the idyllic land"
"alert in battle"
"Mann's people, son of the man"
"from the province of Daron"
"immortal, eternal"
"the number seven"
"praise (from Hallelu)"
"independent wanderer, one who plays by their own rules"
"little fire"
"king"
"God is gracious (via John)"
"choice, selection, that which is chosen"
"protector of men"
"gift"
"place of meeting"
"love"
"sanctuary, sacred space"
"from the heath, heathen land"
"he gave"
"rose"
"sun god"
Similar sound: These names share phonetic patterns with Arcaius — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Greek origins, giving them the same cultural heritage as Arcaius.
Rhythm: Arcaius is a 3-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.