I already knew this manga wasn't going to be one of those "everything is going to be daijoubu" positive thinking encouragement ones, but goddamn, this chapter.
It's a suicide method. You make the room air tight with tape (ie blocking airflow of the windows or doors) and then use the charcoal in a portable-stove which will cause the room to fill with carbon monoxide which can kill you. (not advice for dying, just explaining the joke for the chapter). https://www.wikidoc.org/index.php/Charcoal-burning_suicide Actually I should probably not search this shit up, now my search history looks sketchy..