
Quick answer — Mirai Shida voices Arrietty in The Secret World of Arrietty, Melissa Shield in My Hero Academia: Two Heroes, Miyo Sasaki in A Whisker Away and 1 more characters.
Mirai Shida voices Arrietty (The Secret World of Arrietty), Melissa Shield (My Hero Academia: Two Heroes), Miyo Sasaki (A Whisker Away), Kayo Horikoshi (The Wind Rises).
Arrietty is voiced in Japanese by Mirai Shida.