The art of unarmed combat is something that all bushi appreciate, although not all pursue it in the dojo. Many rely upon the weapon-based techniques they learn from their sensei to defend them even without their weapons, and while this can be marginally effective, the actual study of unarmed combat is much more useful. Monks in particular devote a great amount of time to the art of hand-to-hand combat, believing they both one the body and unify it with the mind.
Jiujutsu can be used as a Weapon Skill, rolling Jiujutsu / Agility against an opponent's Armor TN to hit and rolling a number of dice equal to your Strength, keeping one for damage (so if you had Strength 3, you would roll 3k1 damage for an unarmed attack). Jiujutsu is also used for initiating and maintaining Grapples. The Improvised Weapons Emphasis allows you to use almost anything you can get your hands on to increase your capacity to inflict damage. The GM is the final arbiter of what damage a particular improvised weapon inflicts, but generally it should grant additional rolled or kept dice, but not both.