It was serialized in Shogakukan's seinen manga magazine Weekly Big Comic Spirits from March 2003 to February 2011, with its chapters collected in 15 tankōbon volumes.

Trepanation is the procedure of drilling holes in a person's head, supposedly increasing the circulation of blood and helping to improve the pressure inside one's skull, bringing out a person's sixth sense and causing them to gain superhuman powers such as ESP, being able to see ghosts, and controlling objects remotely with one's mind.

For two weeks, he has declined his fellow homeless men's invitations to set up a tent with them, preferring to sleep in his car.

However, when his car is towed, he agrees to let medical student Manabu Itoh drill a hole in his skull in exchange for ¥700,000.

Homunculus, written and illustrated by Hideo Yamamoto, was serialized in Shogakukan's Weekly Big Comic Spirits from March 17, 2003,[6][7] to February 21, 2011.