Early on in Nioh, after you slay the executioner, players will be prompted to pick their weapons and Guardian Spirit. This being will accompany you throughout the duration of Nioh, offering base increases to a single stat along with giving William a powerful ability that will last for around 10 seconds. This move is briefly showcased in your last fight, however, the potency is notably turned down. All of these Guardian Spirit (aka Living Weapon) skills will make William invincible for around 5 to 6 seconds once activated.
Kato is a Guardian Spirit you can pick from the start of Nioh, and it takes the form of a flaming white wolf. The base increase is +1 to your Strength skill (which is perfect if you picked the battle axe as a starting weapon) and will significantly increase your damage output (20%). This means that you can cut foes down quickly if you’re in a pinch and need an extra boost to your damage. Against bosses, it’s a fantastic way to exploit either a stunned foe or to finish them off when your health is low. If you want to have a big power boost, then make sure to nab Kato.