I can see the appeal of just copy/pasting the Sekiro flavor text, but I believe it's bogging you down. There are things that don't translate well, or at all, to our systems. Notably, you omit crucial descriptive details about how a modification would actually look, how it manifests, or how quickly.
Another thing to keep in mind is that versatility isn't always going to be your friend. Bukijutsu no longer gives benefits to all weapons, only the weapon type you have chosen. Your chosen melee weapon is Katana, which means you won't get boosts for using Axe of the Monkey, Broken Horn, Blade, etc.. Shurikenjutsu will help you while using the Shuriken Wheel, but not the Long Bow, etc.. Mentions of being a "skilled user" are, thus, probably going to do more harm than good.
Let's go through this step by step.
Shuriken Wheel: mechanical device made by the mechanical genius Dogen. Can be fit into the Shinobi Prosthetic to become a working Prosthetic Tool. While it is palm-sized, a surprising number of shuriken can fit into the Shuriken Wheel, as the edges were designed for stacking. A fine example of what can be achieved when one matches mechanical finesse with a Shinobi's talent. Small
I believe your intention with this one is to rapidly draw shuriken to throw (akin to Summoning: Lightning Flash Blade Creation
). I'll need to see that technique registered and approved before I can judge this adequately. Additionally, how many can it hold?
In theory, these aspects might
make this worthy of being mastercraft alone (in the case where the aforementioned technique costs chakra).
Tags Wheel: Tags from across southern seas. Can be fitted to the Shinobi Prosthetic to become a Prosthetic Tool. This wheel posses several tags with different uses, it posses 2 Smoke tag, 2 Flash tag, 2 Explosive tag, 2 Sound tag, 2 Concussion tag, and 2 Shrapnel tag. Sold by Shinobies to raise funds for their travels. Small
Similar to the Shuriken Wheel, the novelty of this modification is the ability to stealthily or quickly draw the tags. To create the tags themselves, they will need to be crafted by someone with the [Pyrotechnician] Trait or otherwise already be part of your equipment.
Axe Of The Monkey: A heavy, black iron axe used by shinobi. Can be fitted to the Shinobi Prosthetic to become a working Prosthetic Tool. This boorish axe is used for cutting and for breaking things with its weight. Once the favoured weapon of a shinobi known as the "Bounding Monkey of the Sunken Valley", it was lost along with his left arm. Heavy
With this, and others, I'll note that you don't have any damage bonuses listed in the first place. Additionally, the Heavy keyword does not give uniform bonuses to damage, you'll have to specify how much extra damage is dealt.
Broken Horn: Famed horn-spear once used by Gyoubu Masataka Oniwa. Affix to the Shinobi Prosthetic to create a Prosthetic Tool. The horn contracts to pull enemies in, also capable of stripping crude armour. When the horn was broken during the rebellion, Isshin praised it for its "splendid shape", awarding Oniwa with the cross-bladed spear of Shuzen Tamura. Versatile Armor Piercing Ignores 10 of Armor.
This is mostly fine but, as mentioned just above, it has no damage values as weapons do. That aside, how big is this thing? I assume you want it to be comparable to Sekiro's, but it doesn't at all read that it would be that size based on this description.
Blade: A Prosthetic Tool made with the blade Of Sabimaru, allowing for a quick series of attacks together with the sword. This tool was used for assassinations and for decapitation, used only when in the act of stealth and within the shadows. Agile | Armor Piercing ignores 10 of Armor.
Like above, this has no damage values as weapons do. However, blades like this are not armor piercing weapons, you'll have to find something else.
Iron Fortress: An iron fan made in the far west. Can be fit into the Shinobi Prosthetic to become a working Prosthetic Tool. Experienced iron-ribbed fan users can deflect shurikens, senbons, kunais, arrows, also counter attacks from both blunt and edge weapons and even high speed attacks using this tool. Passed down through generations of assassins serving the great five nations, it wouldn't be surprising if the next owner decided its weight was impractical.
Seems fine. If you're gonna use the flavor text for impractical weight, however, I'd give it the Heavy keyword. Also, if you want this to be done quickly, I'd say so. This goes for all of them, really.
Long Bow: A Metallic silver long bow made in the far east. Can be fit into the Shinobi Prosthetic to become a working Prosthetic Tool. The user gains 1 tier in Strength for the first arrow shoot within a distance of 15-20m, within that rage the arrow ignores 10 armor. This long bow was used for skilled archers of the war era, to kill leaders and bingo book shinobies without coming Into contact with the opponent. Armor Piercing Ignores 20 armor.
The Armor Piercing is a component of the arrows used with bows, not the boy themselves. That aside, you still need to get rid of Strength boosts from this thing and replace it with actual damage values.
Spiked Chains: An steel chain with spikes in each end of the chain. Can be fit into the Shinobi Prosthetic to become a working Prosthetic Tool. This chain can be extended and retracted, the chain reaches a length of 5m. This chain was used to trap enemies and tie them up while cutting then in the process, skilled users of the spiked chain would fight user at a distance to slow them down then go for the kill. Disarm/Trip | Binding
Mechanical Barrel: A mechanical metal barrel that can be launched at the opponent, capable of splitting blouders and breaking bones. It appears to have been made to fit perfectly inside the wrist bone of the Shinobi Prosthetic. This metal barrel was used to break through defense. Loading 2 post to reload without being interrupted.
Breaking bones sounds like a matter of dealing damage, so it'll have to have some. Additionally, is the barrel launched out as a projectile? Is it more of a piston style thing? How does it work?
This, by the way, can probably have Armor Piercing.
Finally, how do you envision that these prosthetic tools are interchanged? Can you load them in combat? Do you have to do it without being contested? Must it be done in a friendly village? Perhaps by the crafter?