So as always with the Shimura Family Plotline, hand placement is key. Tenko killed Kotaro by placing his hand over his father’s mouth/face. Shigaraki in turn wore his “father’s” dead hand over his face. After All for One shattered Shigaraki in the final arc, he covered his mouth with hands to silence the screams. In BNHA, a character covering another character’s face is a symbolic act of suppression.
Kotaro slapped Tenko across the face. He was often depicted with a large hand outstretched as if to suppress something because that was how he looked in Tenko’s memory. And Tenko reciprocated by covering Kotaro’s face in response. I do think Tenko intentionally touched Kotaro and wished him harm in this moment, but I find it highly doubtful he intended to kill Kotaro. It’s hit or miss whether Tenko even understood the permanency of death, as that is typically learned at around five to seven years old. A person too young to understand that death is permanent can’t intentionally kill anyone because they don’t understand that death is final.
There is a sad parallel of both father and son dying in largely the same way, with their voices suppressed after lashing out at the world in the ruins of most of their loved ones.
