So, I have no idea how we'll get there, and it's probably a slow burn 'in a future far far away' kind of scenario, but hear me out —

One of the defining experiences of Lan Wangji's life was the Sunshot Campaign, where everyone and their mother suffered some kind of war-linked trauma. It was honestly an entire generation of... tragedy and child soldiers and... fun times! But, yeah, if he ever gains a sense of Finn having war-associated trauma, he would genuinely try to help, because... been there. Lost a house and many a clansman to it. War sucks.