[Update] This track has been released on the 2nd OST and it’s part of the song a／z-p1@n0：adlib3
The song plays in Ep. 17 of Aldnoah.Zero (Ep. 5 of the 2nd Season) when Inaho explains to Yuki his motivations of staying a soldier. It’s and extended version of what you can hear in the last episode of Season 1 which I’ve also covered here: https://www.youtube.com/watch?v=PteQadB057E
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