Senjutsu (lit. "Sage Arts") is a technique used in High School DxD.
Senjutsu is different from magic and sorcery. The biggest difference is that Senjutsu stresses the importance of something called chakra, the aura that is the great original power that flows into one's spirit, in other words one's life-force, and turns it into a constant current. It is a power that is both similar yet different from the magic of Devils and the light power of Angels. Its direct destructive power cannot match that of magic or the power of light, but Senjutsu can make use of the unknown part hidden within plants, animals, and people. For example, if one learned Senjutsu, it is said that they could excel at reading the flow of someone's spirit, of their aura, and that they can also grasp the movements of a faraway target to a certain degree.
The Senjutsu, however, also possesses a fatal flaw. While Senjutsu allows the user to read and handle spirit energy, it also takes in the malice and ill will that floats in the world, therefore should an amateur use it inappropriately, the malice will corrupt the user.
Senjutsu is the power to control the flow of life energy. By controlling the flow of ki, a person could strengthen physical bodies or cause vegetation around them to bloom or to wither. Knowing Senjutsu allows the reading of ki and auras and to spy on the target's state from afar. Disrupting the opponent's ki or severing it can cause direct damage to living things. There are very few ways to defend against Senjutsu.
Koneko has stated that Bouchujutsu, a.k.a. the Bedroom Method, a.k.a. "having sex", is the best way to utilize Senjutsu's healing properties.
Senjutsu masters also have the power to use Touki, and use it to enhance their strength, speed, and toughness.
According to Kuroka the most basic way of learning Senjutsu is through meditation by concentrating on the user's state of mind and to quietly release their own ki as well as to sense the natural ki of their surroundings, it is also the best way to develop one's skill in Senjutsu.
To use Senjutsu, the users commonly concentrate their life force around the hand and use it to attack the opponent. The method to attack using Senjutsu may be in the form of hand-to-hand combat or blasting the power towards the opponent.