Sadako sits next to 4 phonetic neighbors — Sadako, Sada, and Kazuko are the closest matches by sound. Most share Sadako's Japanese cluster, so the rhythm and vowel shape carry across the list.
You searched for names like
"upright child; righteous child"
"graceful, beautiful"
"elf guardian, noble protector"
"powerful one"
"the third month, heralding spring"
"from the kingdom of Lothar, from the Lorraine region"
"land of silver, silver-rich"
"bright, shining one"
"renowned warrior"
"from Denzell (estate in Cornwall)"
"rose, flower"
"lion-like"
"One who tends or holds; occupational name related to tenner"
Similar sound: These names share phonetic patterns with Sadako — similar vowel sounds, consonant clusters, or rhythm.
Shared roots: Several names on this list have Japanese origins, giving them the same cultural heritage as Sadako.
Rhythm: Sadako is a 3-syllable name. Names with the same syllable count tend to feel interchangeable when you're narrowing your list.