Well, this one was really hard for an 12th Nani November question, @VinMcCarthy! But, since the last 3 of my cards have had multiple parts, I feel I should really try to pare this down to one! So, here it is, my most favorite technique: Iki Hiyori's Jungle Savate!
The Jungle Savate is not an uber strong technique, nor does it have any flash and bang like most any others in anime. It is basically just a simple roundhouse kick. This is probably a fair ways off what was anticipated for this question, but let me explain. This technique is my favorite not for its beauty or power, but for the wielder and their reasons for its use.
Hiyori is just a simple girl. She's not a ninja with egregious amounts of Chaka and a goal to train to be the Hokage, or a Substitute Soul Reaper with overwhelming soul force that is the only one who can defeat a Soul Reaper-turned-Hollow intent on destroying the entire world. She is a high school girl who enjoys watching martial artists in her free time. When she is plunged into a world where there are suddenly giant glowing monsters everywhere out to eat people, she is understandably shocked and a bit afraid. But, when she see's Yato, still basically a stranger, about to be pounced on by a huge toad-like monster, her first instinct is to run forward and help. And with her being a simple human (albeit a spirit at the time) with no special jutsu, magic, or weapons, she just jumps up and roundhouse-kicks this critter into next week using the Jungle Savage technique she learned from being a closet-martial-arts fan!
So, the ability itself is fairly weak and mundane, but it is spectacular in that it was used at all. Most female characters in Hiyori's position (no power, just first getting a taste of whatever world they are thrown into to jumpstart the plot) would be cringing, yelling at the main male character to run while clutching at their chest. But Hiyori ran towards the danger to help, even though she had nothing but her arms, legs, and spirit, and used this comparatively ordinary skill to help someone in danger. And that is the true power of my favorite technique, not for its amazing style, but it's badass purpose and that purpose's equally badass handler!