Moin, I wanted to ask if The Testament of Sister New Devil is planning a sequel, because the anime was very popular on Netflix.
Very unlikely. Studio is broke.
How popular on Netflix is itchy, the industry is almost exclusively based on the Japanese market. Anime popular in Japan like Date a live, is infinite stratos, fate / stay etc. Get several seasons.
I do not think he will get another season. He has sold ok as far as I know.
Studio is bankrupt and the Novel is at night departures a hentai, which is not animated. There's nothing more