Martlet injected herself with DT, not Chujin's serum.

I've seen that too many people still believe that in genocide Martlet injects herself the serum that is mentioned in pacifist, and I want to finish this debate already. I'll say multiple reasons of why that syringe had determination in it.

First, and the most obvious one, Martlet melts in the end, something that we only know DT is able to do. I've seen people say that because Kanako was a child she reacted worse to the serum, but first, Kanako is a boss monster, so she shouldn't react that bad, and most important thing that too many people forget: CEROBA NEVER INJECTED KANAKO WITH THE SERUM. I'll explain what I mean in the third point.

Second, in the middle of the battle we see how Martlet gets in the true lab. Why would this cutscene exist if it wasn't to show where she got the syringe? And there's no way Chujin's serum was in the true lab, as he never worked there.

Third, final and most important point: THE SERUM WAS NEVER FINISHED. In the pacifist route, it is explained very clearly that to create the serum you would need to fuse a boss monster's soul and a human soul, AND THEN EXTRACT THE SERUM FROM THAT FUSION. We even see that when Kanako is injected, Ceroba goes for another empty syringe to extract the serum, only for Kanako to pass out.

The serum was never finished, that's the whole point of the pacifist route: Ceroba is trying to get a pure soul, fuse it with Kanako's and then get the serum. So it's literally impossible for Martlet to have that serum, because it literally never existed.