"Artificial Respirations"
In English or at-least America, we call them Rescue-Breaths. Sometimes a person in an emergency has an effective pulse (for now) but their breathing is dogshit (barely breathing because of slow rate and/or low tidel-volume). So assisting in breathing by giving effective Rescue-Breaths could be enough.
Also the MC, if you noticed, pinched the Demon Twink's Nose while using his pinching-hand to tilt DT's head back and lifted DT's Chin up with his other hand. This is to:
• Make sure some of the Rescue Breaths don't escape through the nose and go straight to the lungs.
• The Head-Tilt/Chin-Lift Technique is done to prevent the victim's tongue from relaxing backwards and occluding the airway (the alternative technique is the Jaw-Trust).
This is a great manga lmao.