This manga is called Akumetsu.
Its about a guys exerting "Justice" on people who are evil especially the politicians, high rank police officers etc. He killed them in every cool possible ways and died along with his victims everytime.
so let's spoil... Akumetsu is actually clones from the richest guy in the world who was dying. He wanted to create an ultimate body, but he was killed by his own clone. His plan was to clone himself and send them out gain knowledge then transfer back to a single body to becomes the ultimate Akumetsu.
After the ultimate clone is complete, the clone fell in love with the sciencetist and killed the original. The clone died, however the clone factory is still operational.
Akumetsu are a group of clones uniting. They share the same memory and was kept inside a databank. Everytime they died, the mask they wear send their knowledge back to the databank.
Akumetsu can do pretty much everything because his memory is packed with experience of over 150 people. His ideal of justice however is from one of his friend who died from a rare disease.
In the end, all the clone are killed after the clone factory is discovered and raided on. To save the class mate one of the clone fell in love, he transfer all their knowledge to her.