It’s scheduled for an August 31st, 2018 debut in separate formats where it’ll be in Japanese and German with German subtitles.
The light novel series began in 2012 and has ten volumes out so far in Japan.
With two seasons behind it and eleven light novels, we learned last year about the new OVA series under the header Departures for Testament of Sister New Devil.
The anime is adapted from the light novels of the same name that come from writer Tetsuo Uesu.
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The Testament of Sister New Devil - Departures - Clip #02 (dt.)