I do like decks to at least care about the commander so it seemed well fit for that, but it really seemed like the deck would lead to more narrow choices. That is, I obviously want things to have attack triggers so that is what I would focus on. Which is almost too much of a focus.
Interestingly, the commander that led me to wanting to try out a Boros deck was....Yoshimaru, Ever Faithful. I will admit that a pretty large part of wanting to build with this particular commander is based on the flavor text but I started to realize that this wasn't that bad of a commander. Especially when paired with Rograkh, Son of Rohgahh. I chose Rograkh mainly because he is 0 cost so it basically ensures I have a 2/2 commander every game. I know that isn't game breaking (Isamaru, Hound of Konda exists after all) but it seems like this could scale pretty well. And of course he is red so he offers me the color combination I want. I did look at Vial Smasher the Fierce as a way to get Black in there too but I felt this was a better fit.
Importantly, the addition of Rograkh also leads me down the path of trying to go for an Equipment subtheme. It is something I tried with Gisela and it worked decently well, but never felt the greatest. But it seems better here. I can focus on smaller Legendary permanents to trigger Yoshimaru and I can then buff my creatures with cheaper equipment that lets Rograkh do a bit more damage as well.
With all of that being said though, as I tested that option, I found I just didn't like it. There are comments in this thread for when I tried that out and I just find that the equipment packages are not really for me. I had it in Gisela which was fun but it never seems as fun as I like it to be.
So, after further testing, as well as numerous suggestions and discussions with others in this thread, I decided that Jeska is the superior Partner. She not only really pushes me in a different direction than Equipment (Rograkh really wanted that since he isn't that great without it) but she also ends up being faster than Rograkh can be or even than Kediss (my other option) could be. She is a bit more focused than Kediss which can be a bad thing, but aggro really wants to not have to fight against 3 opponents so getting rid of someone early can really help.
I do realize that this deck sort of hits against some of the issues I initially thought of for Isshin. That is, it seems more on rails without a ton of freedom but I don't think that really fits here. Yes, the deck is mostly about Legendary permanents but there are a lot of options to choose from in that regard. I will admit that the mana base sort of builds itself due to the lack of really good Legendary lands but the rest of the deck can be built a number of different ways to take advantage of Yoshimaru. And, with Jeska as the partner, that opens up even more options I think to do a bit more with the deck.
I have decided to go the route of making the deck as fast as I can while still being fun for me. This is mostly due to the fact that I am not an aggro player. I am control and basically every deck I have shows that my tendencies for control dictate the builds. In this case I wanted to forgo that and just try to win as fast as I could without worrying about my opponents. Since I can't truly do that, there are pieces in here that expect interaction but for the most part I am trying to get a big Yoshimaru to kill people with.
I might scale back some of the aggressiveness if I find that I am unable to win a game after knocking out 1 or 2 people (which is an issue I had with a Voltron style Rafiq of the Many deck when I first started Commander/EDH). This is one of the main issues with this type of deck: I have no doubt I can consistently kill 1, maybe 2, people each game. But winning is another thing entirely. And likely comes down to good threat assessment at the start to determine who to take out first. I like control because of this aspect of knowing an opponent's deck to get an advantage and this mindset falls into the same thing to an extent.
I am still working out some of the details but I have a fairly fleshed out list for Shanid..
Here is the current decklist: