Your Oc and Emiko were fighting against villains. They were in a bad situation and if they didn't get out of this fast they would probably die. One villain, who's quirk was a quirk that could release gas, gave the girls a moment to run while the gas surrounded them. When the gas cleared all was left was an illusion of their dead bodies. The villains thinking they won retreated and the illusions disappeared. The girls are now (just to the 1-A students) presumed dead.

How will crush (and Todoroki) react when they are told the fake news?

How will Oc (and Emiko) get back to them without being recognised?

How will they react when they are reunited?

(Aizawa knows the girls are alive but to keep them safe he is keeping quiet)