Eren stopped truly smiling after his mother died.

Mikasa hadn't noticed at first – and neither had Armin – because everything was one big mess of misery and starvation after that head had shot up over the wall. They didn't have food, they didn't have parents, they didn't know what to do. One wasn't allowed to join the military when eleven, and joining the military – Scouting Legion, always Scouting Legion – was the only sort of plan they had.

Because they had to. Had to avenge Carla's death and had to survive, be more than just livestock, trapped inside a wall with slowly thinning grass.

But there was a waiting period, and they didn't know what to do with it, so all they could do was survive – barely, not honestly – and hope that they would wake up after night turned morning. Pretend to be grownup when shaking inside. That was their life now; poverty and scorn, and it encompassed everything.

Then they lost Armin's grandfather almost a year in – they had lost Grisha long before, and none knew which was worse, death or abandonment – and what had been hard before turned outright unbearable.

They bathed in the river – cold all year round – and ate food that had gone through more hands than was advisable, three kids and a book in a world where curiosity meant death.

They ran from the police – part of what they were going to be, but not what they wanted to be – because no one liked scruffy kids without homes or guardians. Especially not ones that looked like they did, angry and frightened and so goddamn stubborn.

I bet they stole it, can't be up to any good, fucking disgusting. Shouldn't have let them in in the first place, should've locked the gate fucking closed. No one would notice if a couple of strays went missing, now would they?

Eren had to kill again – had to, or it would have been them in the burning pile, bones to ashes to dust – and Mikasa helped him dispose of the evidence and both pretended that Armin didn't know. Armin shouldn't have to know – he was startlingly untainted in this world, and they were not – but Armin always had been too smart for his own good. He pretended with them, though, and they were all actors in a play forever a tragedy.

No, Mikasa didn't notice that Eren had stopped smiling – with his eyes and not just his teeth, sharp and harsh but not yet noticed, what they don't know can't hurt them – until they had been military trainees for almost a half a year, and neither had Armin.

After all, it wasn't like they had been smiling truthfully, either.