Mervin sits next to 3 phonetic neighbors — Marvin, Merlin, and Melvin are the closest matches by sound. Most share Mervin's Welsh cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"marrow of the sea, sea fortress"
"God is gracious (via Shawn/Sean/John)"
"fiery one"
"son of the prince (elaborated form)"
"born from the ocean, son of the sea"
"dark one"
"island meadow"
"of the Dorians"
"cooked rice, meal"
"son of grace; graceful"
"doorkeeper, one who ushers"
"heri (army) + beraht (bright)"
"blessed"
"leopard, swift and agile"
"God is gracious (from Shawn/Sean)"
"peaceful ruler"
"Son of Walter"
"powerful leader"
"iron"
"from the rust-colored estate"
Similar sound: These names share phonetic patterns with Mervin — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Welsh origins, giving them the same cultural heritage as Mervin.
Rhythm: Mervin is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.