As has been stated previously the FF Samurais have been mostly based on the versions from Japan's history and many FF games draw mainly from their own history and rarely from outside sources. So when designing any class you should look to FF first and then the rest of the world second. With that said there are precedence for a more supernatural Samurai.

The Samurai of 11 were dispellers of demons. They had the warding circle and demon killer abilities. The Samurai of FF Tactics were even more on the spiritual side of things. They had the ability to "draw out" the spirits of a Katana for some sort of AoE ability. I think we could possibly come to a compromise between the old school honorable warrior and the supernatural destroyer of evil spirits.

I am intentionally not specifying things like potency as these are all just ideas that would need to be balanced by a SE.

This class should retain many of its weapon skill names from 11 and could use them to combo with. Things like Tachi:Enpi > Tachi:Jinpu or Tachi:Yukikaze > Tachi:Gekko > Tachi:Kasha. Each of these combos would have 2 additional effects. One would put some sort of debuff on the enemy like slow, or bind, or an elemental weakness(this is your reference to the FF11 Skillchains). You could name these additional effects after the old Skillchain names. The second effect would weaken and steal a portion of the enemies soul.

One of the primary mechanics would be the Samurai absorbing the soul of its enemy into its katana. This would put a stacking debuff on the enemy that has a small but incremental effect and would place a buff on the Samurai that would do two things. One would be to place a buff on the weapon used that did something specific to the type of creature who's soul was absorbed. Every successful auto attack and weapon skill would absorb a portion of soul, while a successful combo would absorb a larger portion. These soul points would stack up to a certain amount that would increase while leveling. Some examples of absorbed souls could be extra fire damage from a demon, aoe life steal from undead, or increased armor from stone based creatures. The second effect would be that these stacks of soul points would be used as a resource.

These stored up soul points would blast out from the Samurai in a more powerful effect based upon the soul absorbed. This ability should be on a semi long cooldown and expend all of the stored up soul points. This can create all sorts of utility based on what is being fought and could possibly create some unique situations in boss fights with different types of adds. There could also be an ability to instantly absorb a large amount of soul point from a target. That should also be on a semi long cooldown.

I feel the honorable dueling of your opponent is what should be taken from the Samurai's history, so I would be inclined to have some of the positional requirements of skills to have Samurai in front of it's target. This would create the need to move out of the way for tank busters so the class feels a little more action packed and still maintain the honorable duel feeling.

This has some old stuff and some new stuff and also adheres to the established FF lore. What does everyone think?