Senjutsu (lit. "Sage Arts") is a technique used in High School DxD.
Rias explained that senjutsu is different from magic and sorcery with the biggest difference is that it stresses the importance of chakra, their aura, the great original power that flows in ones' spirit, e.i. their life-force and turning it into a constant current. Senjutsu is a power that is similar yet different from the magic of Devils and light power of Angels. Despite it being incapable of matching the direct destructive power of magic or light, senjutsu makes use of the unknown parts hidden in plants, animals, and people. For example, if one learned senjutsu, it is stated that they excel at reading the flow of someone's aura, thus letting them grasp their movements from a far distance to a certain degree.
Senjutsu, however, has a fatal flaw, as while it lets the user read and handle spirit power, it could also take in the malice and ill will that flows in the world therefore if an amateur used it in an incorrect manner, then the malice will end up corrupting the user.
Senjutsu is the power to control the flow of life energy or ki in living beings. Using it, one can strengthen both their internal and external bodies or even cause vegetation around them to bloom or wither. Senjutsu users are able to sense the ki and auras of others thus letting them track targets from far away distances. Through disrupting the ki of their opponent's ki or severing it, it is possible to cause direct damage to their spirit and using this as an attack could result in killing their opponent. As such, there are very few ways to defend against Senjutsu.
Senjutsu also has healing capabilities that are effective for either one physical or mental condition, releasing any fatigue and goes as far as to store one's lifespan, however, this method requires physical contact. Koneko states that Bouchujutsu (lit. Bedroom Method) is the best and fastest method of using the healing abilities of senjutsu, Koneko explains this method is when a woman who specializes in using ki shares her ki with the man and heals their life-force to a greater extent.
In Volume 7, Issei elaborates that Kuroka used senjutsu to tell he was a virgin after licking his cheek, however, it is unknown if she were serious or if she was just teasing him.
Senjutsu users also have the power to use Touki, and use it to enhance their strength, speed, and toughness.
According to Kuroka, the most basic method of learning Senjutsu is through meditation by concentrating on their 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, 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.