Renly's Courage

When the fight with the Dark Territory broke out in Sword Art Online: Alicization - War of Underworld, Renly was terrified and fled from the battlefield. It was not until he saw Kirito's determination that he took up his Twin Wing Blades and decided to fight. He then made his way to return to his unit, but he faced resistance from the goblin chief. Renly was able to achieve perfect weapon control and won the fight. From there on, he battled with courage and was no longer afraid to carry out his duties as an Integrity Knight. 

Renly accidentally killed his dear friend in a sword fight, which I am assuming was the Four Empire Unification Ceremony. His friend's blade broke when they clashed swords, and he was cut down in the process. Renly became afraid to fight from this point on. The Pontifex called him a failure as a knight because he had not yet achieved perfect weapon control. After Kirito, Eugeo, Alice, and the others defeated the Pontifex, Renly was awakened from the Deep Freeze he had been placed in due to his shortcomings in battle. 

When Renly recalled his memories of his friend and their fight, he did not appear to be a knight quite yet. I believe that Renly might only carry this memory alone, just like the other Integrity Knights carry small memory fragments of their pasts. If this is not the case, then Renly may actually have his memory of his past life before knighthood. Knights that are placed in Deep Freeze are "reset" upon awakening, and their memories start with a clean slate. Renly had not yet reached this point, but perhaps his module was removed before freezing for the Pontifex to adjust it and reset it. This could explain how he remembers such a vivid moment. The other Integrity Knights cannot remember the faces of their loved ones in the small memories they hold. Deusolbert cannot recognize that the woman shaking him awake in his dreams is his wife, while Eldrie does not realize he sees his mother in his memory piece until his death. For Renly to realize that he did kill his friend would mean having access to more pieces of his past.

Renly found his courage in Kirito's will, and he decided that his army needed him. No longer did he want to run away from his past and live with regret. As the war continued, he fought honorably and carried out his role as an Integrity Knight.