May These Leaden Battlegrounds Leave No Trace, Vol. 2 (light novel‪)‬

WHY DO THEY FIGHT?
In their quest for a world without war, Rain and Air have been reprogramming history itself by erasing key figures with the Devil's Bullet. But when the two are assigned to a transport mission guarding next-generation technology, the arrival of a powerful new enemy leaves Rain wounded and stranded-and his only chance of survival is to cooperate with his attacker. They'll need to use the Devil's Bullet to get out of this-but on whom?