Grandpa

Mingchao’s grandfather had raised her since she was a baby. He was the creator of the Eto Gun and is an immigrant from China. When he died, he left the gun to Mingchao, but he took the secrets of the gun with him to his grave. He sometimes appeared to Mingchao as a ghost or in a dream, giving her instructions or information about the gun. Apparently he wasn't a very pleasant person, but he cared very much for Mingchao. Source: manga