Blood
Blood, as used in anime, is an important visual storytelling technique, but it's used for more than just gore. You'll also notice that blood is used to ground a dramatic battle or a character's raw determination and instinct to survive. It's that level of intensity, that splash of dark red blood, which fans really enjoy for their edgier home screens.
As for the style, there's definitely high contrast used, which gives the blood a nice texture. There's also a lot of detail with the blood splatters on the blade or the slight blur effect used to make the blood look like it's flowing. Plus, a high-res image of a battered hero standing over a rainy cityscape is definitely solid material for a phone lock screen.
