i think it was Marionette, its a webtoon about A circus full of dead people striving off magical strings, theres creatures called Ak'hon's or in derogatory terms for them, Three-Eyes, they are magical creatures that can see in both spirit and mortal realm mixed(If i recall) they look human too but they are deemed too dangerous and only two got away and lived in a circus with an (As the ak'hon deemed) evil conductor of the circus Tonny and the MC has to kill him by cutting the life string