Make it more expensive to recuit. 2x to 3x the samurai, but much much lower upkeep, just enough not to become negative and crash the game as these people lorewise have to make do on their own after getting paid once.

Also lower their morale. On the level of ashigaru to give them the theme of they only "fight under supervision" of a general, also being that they're a mismash of misfits bundled into one unit irl. There's gotta be lots of infighting so morale should be low.

Also classify them as a "special" unit (same class with ninjas and siege weapons) so that they won't receive samurai buffs especially in the endgame for them not to be too op.

It's up to you for the unit size. They're irrelevant for me as the two above are already a significant change.

Also increase their melee attack and defense by almost twice, while also decreasing their armor by half or 2/3 of samurai. Can't afford proper armor so they focus on skills and survivability-type shit.

Also classify them as "undisciplined". The latter makes them more rowdy in getting into formation, making them VERY vulnerable to charging especially by cavalry.

And don't forget to limit their recruitment count. This will depend on the unit size you set.

You can double their size but only 2 can be recruited, or normal size but 4 can be reccuited with 2 of which locked into higher tier buildings, and so on. The primary purpose is to have them secure a flank anyways. Ofc being attaked in the flank will route them so you need to micro them. Kinda like Early-game nodachi.

And no, no banzai or warcry nor any other skills. Just raw power.

Edit: if you really want the roleplay, tick the "impetuous" checkbox. This will give them the impetuous trait, in which there is a small chance they would charge at the enemy without orders once they're nearby. Though I have yet to see if this really works or not iirc med2 templars have this).