From what I understand, word by word:
Hai: Ash
Kaburi: Cover
Otoko: Man
The title means "The man covered in Ash".
Most likely resembles his life full of bad luck, I think the cigarette he smoke at the last panel resembled it too, a life full of ash color.
Thank you so much for that explanation! Can I also ask you what you think about this interpretation from the comment section?
"It means he's going to continue to torture him (in this case, flicking hot ashes on him). The title "ashes on the head" refers to a funeral rite and represents grief or mourning. I think Daichi is mourning/grieving that his ideal guy turns out to be a sadistic freak, but now he's trapped by his love. The suffering begins....
The title is actually a double-meaning: ashes from sadistic sex and ashes on head meaning something has died and one is grieving/suffering from loss."
I like the later meaning more tho. The death of the kind and lonely neighbor, who is now cruel and creepy, he will always be suffered from the memories from childhood, and Daichi, also will be suffering with him from now on
So I read a comment saying the title refers to a funeral rite, but I couldn't find anything about that on google. I think something may have gotten lost in translation with the dialogue too, especially when he was explaining how his aunt loved him and how his life was over after she died. Some comments said that "loved" might actually imply that his aunt sexually abused him, but I didn't get that impression from the dialogue. I hope someone who speaks Japanese can check the original lines and explain them to us.
It's intriguing, though, and I do want to see more chapters. We know this is the start of a toxic relationship. I want to see the point where Daichi stops tolerating Tooru's abuse, helps him heal from his past (the neglect and abuse by his mother), and teaches him how to truly love and be loved.