WARNING: The following contains spoilers for 86 Eighty-Six Episode 15, "Welcome Back," now streaming on Crunchyroll.
The future has been a constant topic in 86 Eighty-Six Part 2 up to this point. Shin and the rest of the former Spearhead Squadron decided to abandon the comfortable and peaceful lives Ernst granted them in the Giad Federacy because they felt they belonged on the battlefield. When Ernst responded that he'd like them to have certain opportunities after the war, they were silent. They hadn't considered the fact that this war won't last forever.
Shin, Raiden, Anju, Theo and Kurena have all been avoiding thinking about the future. Having spent so much of their lives on the battlefield, they think it's only natural to continue fighting until they eventually die. However, the war will end at some point and there is a chance they'll survive. Therefore, they need to start seriously thinking about what comes afterward.
In 86-Eighty-Six Episode 15, the Giad military is preparing for an imminent large-scale Legion attack. According to Grethe, they expect to be able beat back the Legion forces with their current numbers, but Shin has his doubts. His power to detect Legion mechas seems to indicate there will be far more than the Giad military is expecting. He attempts to warn Grethe about this but she finds it hard to believe, and he won't press the subject because he's keeping his power a secret.
Afterward, young Frederica visits Shin's room and they discuss Eugene's death, which has clearly been on Shin's mind. She tells him that unlike his room -- which is virtually devoid of anything personal -- Eugene's room had pictures of his sister in it. She also reveals that her knight, Kiriya Nouzen, was a member of the Nouzen clan like Shin and the two are very similar.
Shin asks her why Kiriya became a Legion, and she solemnly responds it was her fault. Kiriya ended up going insane as he fought to protect Frederica and her family from rebels -- who turned out to be members of the current Giad military. Kiriya lost his family and everyone he knew in the chaos, thus, protecting Frederica became all he had. When the Federacy eventually found Frederica and her family, she was spared but they publicly showed the imperial mantle she wore as proof of her death.
Kiriya saw the imperial mantle and believed Frederica to be dead, leaving him nothing left to live for. When the Legion were wandering the battlefield looking for things they could recycle, Kiriya just stood there and let them get him. This reminded Frederica of how easily people die, and she urges Shin to run if the upcoming battle gets too dangerous. She stresses that saving Kiriya isn't worth his or the others' deaths.
Frederica tells Shin that they all still have a future and it cannot be taken from them, but Shin is once again confused at those thoughts. Channeling a previous conversation Shin had with Lena, Frederica tells him to think about things like where he wants to go on his next leave and what he wants to do someday.
Soon afterward, Shin finds Raiden, who reminds him to keep his power to hear the Legion hidden because the Federacy aren't the saints they think they are. Raiden fears Shin could become their guinea pig if they ever find out about it. Oddly, yet not unexpectedly, he then asks Shin if he's thinking about anything he doesn't need to.
As has been the theme of Episode 15, Raiden is referring to the future. It's almost disturbing how the Spearheads treat their thoughts of the future, as if it's taboo. Shin says Frederica told him to think about it but he never has, because he's never needed to. Raiden mentions it was around the time of the day they'd usually be talking to Lena, and asks if he thinks she's doing okay. Shin doesn't respond, but it's obvious he was thinking about her and contemplating a future beyond war as 86-Eighty-Six continues.