Koi

The Koi (鯉, Carp) seal is a hand seal unique to users of the Onmyōdō, which is required in techniques that use the unique "pure" Yin and Yang nature techniques. This seal is formed at the end of such technique to keep the energy in check and mold it into techniques. This seal remains the same when combined with other techniques, such as Sage Mode (or something resembling it.

Form
The seal resembles the "Tiger" hand seal, but the difference is that the index fingers are wrapped around the middle fingers instead of being hold down like the other fingers.