[Autumn]

If we really have to buff Sheath Sword like this, I'd rather adjust the ranks as such:

Rank 1: Learn Skill, 3M Required, +5 Hit/Damage
Rank 2: User turns against attackers from the sides, +10 Hit/Damage
Rank 3: 2M required, +15 Hit/Damage
Rank 4: User turns against attackers from behind, +20 Hit/Damage
Rank 5: 1M required, +25 Hit/Damage

Considering Fleur, Kensei is already capable of doing two actions before Sheath Sword, and unless Hidden Cut started stacking up how many hits the Kensei landed, we aren't going to see any great impacts if the momentum cost is lowered.

Also, making the user turn against attacks they aren't facing is a good way to give reason for players to actually rank the skill, rather than just going 'whelp no one's putting more than one rank in, might as well make it one point only /shrug'. (Not to mention that Watchful Eye is notoriously easy to slip past, and holds no other benefits to warrant constant use)

With 2 weapons you can get 1m at the end of your turn after critting with both of them, I don't think that's a good idea, considering hidden cut with elemental katana and hisen can hit as hard as fully fledged 3m skills.

And automatically facing you towards the target is just scale Kensei to stupid levels of power vs anyone, it already has that.