Masku:

[quote]As the founder of the Niten-ryu school of swordsmanship, Musashi holds the highest rank possible for it.[/quote]

EX isn't the highest rank.

[quote]It allows the user to completely overwhelm the opponent with quick, powerful strikes. With a Single Action attack, the opponent has two different strikes that they must react to.[/quote]

Keep in mind the drawback if you do something like that, from a combat perspective. That's all I'll say.

[quote]and also receives a damage bonus similar to the one received from Bravery A+.[/quote]

Remove this, your stat boosto is more than enough.

[quote]Additionally, if used between the hours of 09:00 and 15:00, the opponent will receive a one rank penalty in AGI for 2 hours.[/quote]

Remove this and your modifier from Disengage. Your bonus effect is more than enough.

On the oar:

[quote]Combined with Musashi's all-in, strength-supporting weakness-exploiting fighting style,[/quote]

This is covered by Eye of the Mind.

[quote] E-A+++ (Same activation cost as C Rank Noble Phantasm)[/quote]

This doesn't work. When you're saying that this Noble Phantasm ranks up as he keeps attacking, just the aspect of it conceptually ranking up is going to drain you dry by the time you've made a couple attacks as a result of that passive ranking-up. It's like Arondight and Karna has a prana-consuming child and this piece of wood is that child.

Furthermore:

-Why is a piece of wood suddenly a prana furnace? An example of a prana furnace on that tier is a book that is literally alive. Show me why it's a prana furnace in the legend.
-Show me why the piece of wood can suddenly shoot a beam that can theoretically beat Excalibur in power, and since there's no cap on how high the numerical value can go, Ea as well.
-Show me why it can shoot a beam in the first place when all it was used for was A. weapon improvisation and B. rusemaster-ing.
-Tell me what "A+++" means when A++ is literally at the level of Divine Spirit Thaumaturgy.

The main thing though is that increasing the power of his slash doesn't have anything to do with his legend does it? He wasn't someone who made a super attack at some point in the fight, or anything like this. This isn't anything like the oar. You're literally just taking super-functions and adding them onto the oar as if they're conducive.