Honestly the biggest surprise with Iori and Musashi hasn't been that Iori recognizes his father in an instant even when she's now young again and with huge boobs; it's that this version of Musashi—canonically the same one from FGO and even brings up her adventures in FGO—still has the exact same version of Iori in her timeline without any changes.
All that time cavorting around with Gudako and she never mentions she's actually a mother of two.
Fate/Samurai Remnant has a New Game Plus option, which allows you to jump right back to the start of the game with all your end-game gear and powerups.
It also gives you the option to jump right to the start of chapter 2 - this is where the NG+ specific content starts being available - but you can start from the very beginning. I did this immediately, of course, because I wanted to see how end-game Iori holds up against the Rider fight at the start of the game.
The game forced me out of the fight before I really got to know the answer, but I learned something else along the way. When you first get Saber, your way gets obstructed by a small group of mooks, and Saber dispatches them with an impressive two swings of their sword, each swing taking out half of the group in one hit. This helps sell you, immediately, on the raw power that Saber wields, and how broad a gap there is between Servants and yourself - you'd just been fighting those enemies recently, and know first-hand they take like a half-dozen hits to take down.
But when you start New Game Plus and face the first horde, you realize very quickly that enemies have not been scaled up to compensate. This is a pure New Game Plus experience. And you can see, personally, that an end-game Iori can dispatch in one hit enemies that would take a half-dozen or so when he first began the adventure.
Both Iori and Saber get stronger over the course of Fate/Samurai Remnant, but by the end of it, Miyamoto Iori is - objectively, provably, mechanically - in swinging distance of the power of a Servant.
Emiya: and after i sold my soul to the counter force, i spent the rest of eternity wandering from conflict to conflict, killing over and over until it was clear there is never an end to war and i cant save anyone
That sounds like gameplay wise instead of a pokemon the servant is now an attack dog huh
An attack dog that's far stronger, faster, and tougher than you, able to wipe humans in a flick of the wrist.
Mind you, the effort the game puts into establishing Iori as a highly capable fighter on his own is what makes the sheer power difference in the game so fun. Iori has a full skill tree to upgrade, multiple fighting styles, mechanics for striking enemies at critical moments and for dodging their moves perfectly, learning magic spells, equipment that can grant different upgrades, the works. He's not a guy that has a basic moveset to defend himself, this is a guy with a LOT of ways to fight.
And yet, Saber moves faster, hits harder, and trashes most enemies by themselves. If you think about it, you don't actually have to fight (Saber even says so!), but you can, so you will. You're not going to stand back and let your houseguest do all the work just because they're stronger, right?
So when you meet an enemy that can actually threaten a Servant, like say, another Servant, you instinctively know how bad of an idea it would be to face them yourself. Saber instantly destroys human enemies that you have to throw around for a bit to defeat, fighting someone like that puts you in actual danger of getting killed in a couple of hits.
For almost 20 years Fate readers have seen dudes make the incredibly stupid decision to join in a fight between Servants because they can't sit by and do nothing while someone else fights. In Samurai Remnant, you get to experience this for yourself. You're not gonna leave Saber behind just because Rider takes out half your HP in two hits right?
sorry to go insane about Iori again (that's a lie i'm not sorry), but i was looking through his myroom lines for the 5th time or so and focused on this one
which is triggered by having any of these servants
which, as you can probably guess, is all the summonable servants with extremely high levels of clairvoyance. They are looking at Iori and they know. It's already partially implied in FSR, but the reason Gil takes an interest in him is that he knows.