I am building a custom setting that is medieval fantasy (technology level is almost steam engine) where some pieces of ancient technology (ours) can be found.
Players' weaponry is based off the Monster Hunter weaponry : Long sword, Short sword, Large sword, Lance, Dual-wielding sword, Gunlance, Bow, Bow-gun, Hammer.
One of my player (call him P1) really really really wants some sort of mecha/exo-suit and I said I'd consider it.
The plot context
My idea is that during the main quest (Retrieve a kidnapped Judge and bring him back to the main city) this P1's goal will be to befriend the inquisitor that travels with him (hopefully another PC but I can't force someone to be an inquisitor) as the mafia asked P1 in order to extend their reach. On their way they'll stumble on that exo-suit that P1 will be able to pilot because of reasons.
When they bring back the Judge and the attempt to befriend the inquisitor has failed (or worked but doesn't get P1 the influence the mafia wanted) he tries to rely on force and take over the city using the suit. The rest of the party teams up with one side or the other and they fight over the control of the city. End of the 1st arc.
There will be some time between the moment P1 gets the suit and my PCs start fighting each other so I am afraid that the others will just feel bad/left out.
The suit uses DNA recognition so only P1 can use it. Its abilities would physical enhancement (so a huge buff in Force and Agility. How huge is still uncertain as I don't want P1 to be impossible to beat). Kind of like Batman's suit in Batman v Superman but without the other gadgets.
Only P1 is yet aware that I intend to make him a traitor and give him an exo-suit. The others don't know yet about it and I'd rather they didn't but if it is what it takes for them to not feel bad about not having a suit for themselves then I could talk it out with them.
How do I grant this exo-suit to P1 without having my other PCs feeling left out or making the suit basically so bad it is a non-factor?
I do not want my other PCs to be left out, first and foremost. Having only one of them in an exo-suit while the others are fighting with primitive weapons feels unfair. I want the whole "P1 was working for the mafia all along" to be an actual plot-twist. Therefore, my other PCs would not be aware that the reason I give P1 the suit is because they will have to outnumber and fight him.
Background: how my homebrew game's combat works
My game system is custom but it is mostly based off Pathfinder. You roll a d20 and if it's higher than your opponent dodge/parry score then you get a hit. Stats are the same from Pathfinder except dexterity is called agility and defines your chances at dodging.
A successful dodge results in no damage taken and a replacement of your character. A failed one adds a 20% bonus damage on your enemy hit (a heavy blow is around 5hp and PCs have (8+Const.modifier) HP)
Dodge score is equal to 8 + Agility modifier (if a PC can predict the opponent's next move he gets a bonus to dodge but if he guessed wrong he gets a malus)
A successful parry results in half of the damage being taken as Stamina damage (12+Const.modifier) and half of them as HP damage reduced by your shield size (from 1 to 4)
Parry score is equal to 8 + Force modifier + shield size (A short sword and targe is size 1. A Broad sword is size 2. A Lancer's shield is size 4)