Parallax (Sentient Stars #2) by Amber Toro
 
The tenuous alliances of the United Tribal Axis have fractured, breaking humanity into warring factions. Hinata finds himself fighting a losing war against an opponent that doesn’t play by the rules. While Freyja focuses all of her efforts on uncovering the origin of the signal that she is convinced is the key to revealing the source of the chaos ripping their society apart. Upon returning from an outer rim mission, Freyja realizes that Skyla hasn’t received a single communication they've sent in months and must convince Hinata to abandon his post to mount a rescue mission in search of the missing captain. But there are forces at play larger than any of them realize.