Regan sits next to 4 phonetic neighbors — Reagan, Keegan, and Brogan are the closest matches by sound. Most share Regan's Irish-rooted cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"little king, of royal descent"
"oak grove"
"elevated, sublime, lofty"
"shade, silhouette"
"courteous, well-bred, polite"
"fire brand, flaming sword"
"Yahweh is my strength"
"from the rose field"
"brave in battle (via Casey etymology)"
"broad valley, wide hill"
"modern invented name with phonetic appeal"
"modern blend of Jay + -ren"
"wise counsel and army, counseling warrior"
"spear, warrior"
"solid, strong"
"well-being, blessing"
"prince, ruler"
"related to Everett (brave boar)"
"mountain of strength, exalted"
"elaborated form of Joshua"
Similar sound: These names share phonetic patterns with Regan — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Irish Gaelic origins, giving them the same cultural heritage as Regan.
Rhythm: Regan is a 2-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.