Armin looked at Kurama. "No one knows where the titans came from, but they seem to be made of the same things as humans. Hanji did some tests on some titans she and her team captured and it seems that they are very lightweight but burning to the touch. They do not have hearts or digestive organs but they get their energy from what seems to be the sun. Their blood is the blood of those they have so called 'eaten' by absorption in their internal holdings. The titans, surprisingly from their vast numbers, cannot reproduce, and they are all what seems to be male, with the exception of Annie when she forms into her own titan form, just as Eren here does." he explained.

Eren nodded. "Yeah, but I can only form due to self-injury."

Levi looked at Kurama as well. "Titan skin can only be cut by the blades of our 3 Dimensional Maneuver Gear, which can only be used by soldiers trained with the weapon and gear like us." He grabbed Eren's shoulders and spun him around, brushing Eren's brown hair away from his neck. He drew a horizontal line across the back of Eren's neck. "We have to cut here, slicing out a chunk of the flesh, to kill them."

Eren looked over his shoulder. "It's kind of hard to do, but when you train hard enough, you get the hang of it."