Ryuga's first appearance in Episode 1 is way to make an impression. He stabs a bride at her wedding party, grabs her and smashes through a window only to kill her mid-fall. Naturally, the bride was a Horror.
Sonshi's beatdown of the Knights. With Ryuuga to be the only one who manages to even put a dent on Sonshi.
The visual effects department really pull out all the stops in Episode 18. Scenery Porn is aplenty in the ruins of an old Makai village and the fight scenes... oh my, the fight scenes. Unfortunately, the battle is in favor of Team Tousei.
All of Episode 19, when ALL of the Makai Knights prove themselves to be Determinators, though the cake goes to Ryuuga, who is BLIND.
Episode 21, where after Enhou was defeated, her human body was left behind. With Rian doing a costume change to give her identical clothes to Enhou's combat fatigues, she went to where Takeru and Aguri were facing Rivera and SG-1. Rian, perfectly imitating Enhou, said that the Makai Knights were the allies of SG-1 and that Rivera was the true enemy before firing on her. This caused Rivera to pull a knife and charge at Rian after her Tomato Surprise Reveal, which was exactly the reaction she was hoping to get. Just before Rivera's attack could hit her, she used a smoke bomb to cover her switching places with Enhou's body, and in a massive case of Laser-Guided Karma, Rivera, who had earlier framed Ryuga for murder, was framed for murdering Enhou, and at the same time the Makai Knights had their names cleared.
Episode 23 arguably takes the cake: Ryuga finally managed to restore the armor of GARO to its golden brilliance. The way he was slowly walking forward as the darkness on his armor was purified was just Bad Ass. Of course, then it turned Tear Jerker...
Episode 24: Ryuga fights off Zedom and wins with the help of his friends. Then he tracks down Tousei and with Rian gives him the Karmic Death he deserves since he has became a Horror.