The tempest's blessing, forged; The storm's wrath, sheathed.

The former, inscribed along the edge of the the hand guard (tsuba); The latter, etched along the edge of the mouth (koiguchi) of the wooden scabbard (saya). Both, in Draconic (Auran).

Unsheathing the weapon by someone not attuned to it releases a thunderous crack, dealing 1d6 thunder damage to everything within a 5 feet radius of it. Attempting to use this weapon without attunement deals 1d6 of lightning damage to its wielder with every swing / melee attack made.

Other than the abovementioned, without attunement, this weapon is just a regular Greatsword that has the Finesse weapon property.

Attunement. This weapon must be used to kill 1d6 + 4 medium sized humanoid creatures before it can be attuned to. Large humanoid creatures count as 2 medium sized ones, and huge ones count as 2 large, so on and so forth. The following benefits are only available to the attuned owner of this weapon.

You gain the following benefits while you hold Yamamoto:

• You can speak Auran and Primordial fluently.
• You have resistance to lightning damage.
• You have advantage on saving throws against the stunned condition.

You may have this weapon deal lightning damage, instead of its usual slashing.

Improved Critical. This weapon makes critical hits on rolls of 19 or 20 on the attack.

Life Steal. When you attack a creature with this weapon and roll a critical hit on the attack roll, or deal the final strike to kill a creature, you gain half as much temporary hit points as the total damage dealt for that attack, which lasts until the weapon is either sheathed, or dropped / disarmed. These temporary hit points manifest as a thin layer of crackling lighting energy surrounding your body.

Charges. This weapon has 10 charges. It regains 1d6 + 4 expended charges daily at dawn.

• Lightning Smite. When you hit a creature with a melee weapon attack with this weapon, you can expend one of its charges to deal an extra 2d6 lightning damage to the target, in addition to the weapon's damage.
• Extra Attack. Once per turn, when you hit a creature with a melee weapon attack with this weapon, you can expend on of its charges to make one additional melee weapon attack with this weapon.
• Unstable Charges. When you attack a creature with this weapon and roll a 1 or 2 on the attack roll, you automatically miss the attack, lose one of the weapon's remaining charge(s), and take 1d10 lightning damage.
  If there weren't any charges left to expend, you and everything around you in a 5 feet radius take 2d6 thunder damage, and you are immediately stunned until the start of your next turn. Everyone in a 5 feet radius of you who fails a Constitution saving throw of DC 12 is also stunned along with you, until the start of your next turn.

Flaw. Yamamoto makes its wielder fickle, and prone to erratic mood swings. As changeable as the weather, your moods shift from calm to wild and violent with little warning, but these storms rarely last long. While attuned to the weapon, you gain the following flaw: “I am fickle and indecisive, often changing my mind without much hesitation, for the smallest or pettiest of reasons, or none at all even."

Proficiency with a Greatsword allows you to add your proficiency bonus to the attack roll for any attack you make with it.

Notes: Bonus: Temporary Hit Points, Resistance: Lightning, Language: Auran, Language: Primordial, Weapon Property: Finesse, Advantage: Saving Throws, Damage: Lightning, Stunned, Healing, Damage, Combat, Heavy, Two-Handed, Graze