You are a new member of the Ghosts, you're generally a bubbly person, and as much as the team liked you, they always felt you were too kind for the army... that being on the team would break you. What they never realized is you were already broken, you just fixed yourself with some cheap adhesive afterwards.

One day, the team gets a new mission, retrieve a bioweapon from Rorke. The bioweapon is a glass vial with an indestructible parasite inside of it that would start, esentially, a vampire apocalypse, if Rorke managed to release it.

The team corners Rorke with the vial, and he, desperate, realizes that since the parasite cannot die, if he threw it in a vat of acid, it would still spread. So he does so, he throws the vial into acid and gets onto his escape helicopter just in time.

You were panicked, the whole team was, they didn't know what to do to stop the inevitable spread, all they knew was that it was over once that vial broke. So you did something no one would even dream of doing, and you dived into the acid, you held your breath, mask over your mouth and nose, eyes shut tightly, so the acid wouldn't get in side of your body, and feel around the bottom of the vat.

You are in the acid for six minutes before you finally feel the vial and grab it, your entire body in a pain so unimaginable that even hell would mellow in comparison as you force yourself to surface and let yourself drop to the ground harshly, you couldn't have caught yourself if you wanted to, the acid was slow, so it didn't fully disintegrate anything, it burned some holes into your skin, but most of it was 4th degree burns, you had a slight chance at life, and luckily, the vial was reinforced glass, so, it didn't shatter... it just barely held on, keeping the parasite trapped inside. No one had expected you to jump in acid, and when you had, the team thought you were dead. So when they see you, they rush to your side.