WARNING!!
This story contains: Mental and physical abuse, self harm, gore/bloody scenes, nudity, Stockholm Syndrome, and needles.
Kai Chisaki, also known as Overhaul, created a quirk destroying bullets. To create this, he used the blood of a 7 year old girl named Eri. Thanks to her quirk, called Rewind, the quirk canceling drug completely erases a person's quirk. Everyone, and anyone, who gets hit with one of these bullets, will completely loose their quirk.
Well, almost everyone.
One day while protecting citizens from newly escaped Yakuza members, Shoto Todoroki and Minoru Mineta both get hit with the bullets. However, while Mineta loses his quirk, Todoroki still had his, and shot out ice at the villains. It becomes apparent that Shoto Todoroki is immune to the drug.
This is due to his blood having a never before seen mutation that is classified as a new quirk.
"ᴛʜᴇ ᴡᴀᴛᴇʀ ʜᴇᴀʀꜱ ᴀɴᴅ ᴜɴᴅᴇʀꜱᴛᴀɴᴅꜱ. ᴛʜᴇ ɪᴄᴇ ᴅᴏᴇꜱ ɴᴏᴛ ꜰᴏʀɢɪᴠᴇ."
Most would say that your quirk manifested in a rather unusual way. In an environment filled with stress, it manifested on its own before lives were lost. Water manipulation.
A boy, no older than four, vanished beneath the surface of the sea without anyone seeing - all until the sea parted and he coughed up water in the dry sand.
Named a hero, written about in hundreds of papers, you became the nation's treasure overnight - for saving Endeavor's youngest son.