Rurouni Kenshin Vol 18

He may be one of the "good guys" now (as Misao insists) but, even a month later, Kenshin still is haunted by Kyoto. How can he not be, when it was in Kyoto that, as the feared "Hitokiri Battôsai," he once made the streets flow red...? And yet, before he departs this place of so many memories, there are ghosts which must be put to rest. It's said that, when strong feelings are attached to a particular wound, so long as those feelings persist, the scar will remain. How did Kenshin get that cross-shaped scar on his face, and who was it that gave it to him?