In Episode 12 when Subaru becomes possessed with the spirit of Petelgeuse, Nagatsuki was told that Kobayashi was “strained” voicing the double character.
In the same episode, Nagatsuki was concerned with how Emilia would pronounce “foreign” words.
Nagatsuki felt “quite satisfied” when he came up with Emilia responding with “deito” to Subaru, which also sounded cuter in retrospect.