Alna - Shion Wakayama. She also voiced Momo (Dandadan) and Nanahoshi (Mushoku Tensei), and currently she’s voicing Arte (Okiraku Ryoushu no Tanoshii Ryouchi Bouei)
Dias - Kenichirou Matsuda. He also voiced Glen Garia (Guild no Uketsukejou desu ga) and the narrator in Spy x Family (…and Bond. Woof.)
I checked the voice actors (source, Anilist):
Both are perfect fits.