Haemoglobin binds with oxygen in body locations where the oxygen concentration is high (in the lungs) and forms oxyhaemoglobin. Blood with a high concentration of oxygen is described as oxygenated
hmm ffom what i know, mitsuki is artificialy made by orochimaru hence why we can make multiple mitsuki. and as for kawaki, hes a normal boy who was experimented on by jigen as a possible vessel if im not mistaken