The Samurai, as introduced in Xanathar's Guide to Everything is a cool class that suffers from some minor issues, them being:

• The thing that they really want to do, can almost never be done (only three Fighting Spirits per long rest)
• They lack the versatility resources from other fighter subclasses while not having too much going for them.
• They are outpaced, damage-wise, by the remaining Fighter subclasses only barely catching up by level 15.
• The really cool features come too late (Elegant Courtier at 7, Tireless Spirit at 10, Rapid Strikes at 15!)
  

The last point is particularly exacerbated by the BG3's level 12 hard cap.

This mod aims to fix these issues by mainly moving all Samurai abilities around making you learn them early, enabling you to have a whole Samurai experience by level 12. I also added a few things inspired by D&D3.0 Oriental Adventures, but if you'd rather not have them, just download the optional file without them. I'll mark in italic whatever features are new. Also, bear in mind that BG3 and its game engine cannot entirely replicate the tabletop system, so some things had to be changed.

If you would rather have the 5e Samurai version, as close to RAW as possible, consider my other mod: Samurai Fighter Subclass (Release ready)


Bonus Proficiency:
When you choose this archetype at 3rd level, you gain proficiency and expertise in one of the following skills of your choice: History, Insight, Performance, or Persuasion.

Fighting Spirit:
Starting at 3rd level, your intensity in battle can shield you and help you strike true. As a bonus action on your turn, you can give yourself advantage on all weapon attack rolls until the end of the current turn. When you do so, you also gain 5 temporary hit points. The number of hit points increases when you reach certain levels in this class, increasing to 10 at 10th level. You can use this feature three times, gaining an additional use at 10th level. You regain all expended uses of it when you finish a short rest.

Elegant Courtier:
Starting at 3rd level, your discipline and attention to detail allow you to excel in social situations. Whenever you make a Charisma skill check, you gain a bonus to the check equal to your Wisdom modifier. Your self-control also causes you to gain proficiency in Wisdom saving throws.

Iaijutsu Strike:
Starting at 3rd level, the first enemy you attack each round that you have Advantage takes extra damage, as you quickly draw your weapon and catch them surprised.

*Works like a sneak attack, but progresses slower, has smaller damage dice, and only procs on advantage, however it works with all weapons.*

Progression:
3rd Level:    1d4
5th Level:    2d4
9th Level:    3d4
12th Level:  4d4

No thought:
Starting at 5th level, Samurais add their Wisdom modifier, if positive, to their attack and damage rolls.

Tireless Spirit:
Staring at 6th level, when you roll initiative and have no uses of Fighting Spirit remaining, you regain one use.

Rapid Strike:
Staring at 7th level, you may target an enemy that you can see and that you have advantage against. You enter a furious stance that gives you Disadvantage, thus negating the Advantage, but that enables you to make one free Extra Attack against that target. You must have attacks remaining to activate this stance and can dismiss it whenever you want.

*To avoid exploits, you can only activate this ability when you have action points remaining, and you can only use the free attack when you have no action points remaining. Starting or dismissing it is a free action. The free attack automatically dismisses it, but if you killed your target before using the free attack, be sure to dismiss it before ending your turn or you'll make opportunity attacks at a disadvantage for the round.*

Strength Before Death:
Starting at 10th level, if you reach 0  points, you regain 1 hitpoint instead of becoming Downed and become untargetable until you can act. You can use this feature once per long rest.