I don't know how it's generally called in manga, but blood doping it's similar, and it kind of works like how you described.

Autologous transfusion, a transfusion of your own blood, which is drawn and then stored for future use, artificially boosting the blood's ability to bring more oxygen to muscles and increasing the number of red blood cells, causing the blood to thicken and forcing the heart to work harder than normal to pump blood throughout the body.

Or some special power gained from anemia lol.

more damage at low hp is also referred to as "berserk" in certain games

The more I look into it I'm coming up with berserk having the same definition as what I'm looking for, ill keep searching

wheezes

Just Monika.

Ty monik for the hug.

Holyshit that gif is real.

im in

I'm on it like hell ya.

better start a week early in november then, no excuses

Sounds like a challange.