The Unknown Training (知られざる試練 Shira rezaru shiren?) is an extra chapter of the Attack on Titan: No Regrets manga, written by Gun Snark and illustrated by Hikaru Suruga. It was included in the second volume of the Complete Color Edition, after Side Story 2.
Overview
On Flagon's request, Commander Shadis shows military discipline to Levi, Isabel and Furlan.
Summary
Shadis hits Levi
Flagon and Erwin have a discussion about Levi, Isabel and Furlan, who lack discipline. Flagon's plan is to have Commander Shadis teach it to them.
Later on, Flagon witnesses Shadis meeting the three recruits. He scolds Isabel and Furlan for getting their military salute wrong. When it is Levi's turn, Shadis tries to intimidate him by head hitting him but it does not work. Shadis tries his special hit on Flagon to make sure it still works, which makes Isabel laugh. Acknowledging basic display of authority has no effect on Levi, Shadis decides that from now recruits with this profile would not require to go through the rite of passage.
Afterwards, Erwin meets a still wounded Flagon and observes he is not as tough as he claimed it.