I couldn't miss the chance to practice my drawing!
Ichi no tachi is a Japanese martial arts concept found in older schools of koryu and kenjutsu. Due to the intensity of pre-Edo period combat, it was emphasized that a single blow was the difference between life and death, and was studied from offensive to defensive angles to survive large scale battles. In kata forms, the term refers to the first form generally learned and drawn upon as the basis of one's kenjutsu style, and would guide the practitioner to hone their art to embody their school's philosophies.
For simpler reference, Ninja Slice is evocative of a swift and deadly assassin able to enter, strike, and kill at any time at one's most vulnerable, not unlike being able to finish a struggle off in a single blow.