The Fortissimo (フォルテッシモ Forutesshimo) is a Sitar available to Demyx in Kingdom Hearts 358/2 Days. It can be upgraded to the Fortissimo+.
The Fortissimo has a dark blue, roughly triangular headstock with two small, semi-circular notches taken out of its base. Its neck is dark blue with gold, concave edges. The body of the sitar has an arrowhead shape. The center of the body is navy blue with a large, gold “X” in its center, and the edges of the body are also gold. Its three white strings are anchored to the body by a small, navy blue, heart-shaped piece. If viewed upside-down, the Fortissimo bears an uncanny resemblance to the Heartless emblem. It is nearly identical to the Serenade, though it has a different color scheme.
Musically, fortissimo is a dynamic, represented by ff. It means "very loud."
Fortissimo's ground combo starts with a 360° spinning attack, after which, Demyx strums the sitar, emitting a yellow shockwave which damages any enemies around him, followed by a leap and a very fast airborne spinning attack. The next move of the combo is repeat of the the first move, and is followed by a blast of three yellow shockwaves forwards.
The aerial combo consists of a series of very fast airborne spinning attacks, followed by four quick blasts of yellow shockwaves in an outward direction, and ends with a blast of three yellow shockwaves forwards.
 See also