The Yasakuni Sword can be bought for ten merits.
(can no longer be bought for merits)
It can also be found in the city, and used to be very rare, before it was made available through merits.
Was the strongest Melee weapon in the game, before new weapons were later introduced (eg Dual weapons from the level 35 Mission etc).
Damage multiplier: 1.15 x strength*
* Before attack system change