TL;DR: upgrades to existing specializations for easier item farming and slave acquisition, mid-combat energy recovery, healing and stress relief, debuffing etc.
I was thinking about what would potentially be nice tier 2 specializations for your endgame needs, which are many and currently unsatisfied, and this is what my brain came up with at 7 in the morning.
Since they are fairly OP, I feel something like this should cost you ~5000 gold and take ~10 days to acquire. Also, maybe teaching these specializations would be something only an institution in Amberguard could do, and only if your reputation with this city is maxed out (which, if you have previously been hunting for elven equipment, should not be that much of an issue).
Assassin -> Shadow
+10 Speed, +10 Damage, ordinary attacks and physical skills have a chance of instant KO equal to (slave's level - target's level) percent. Gains skill "Cloak" (enemy units cannot target the user for the number of turns equal to half the shadow's agility stat).
Requirements: Noble, Agility 8, Strength 6, Wit 105.
Bodyguard -> Aggressor
+8 Armor, +40% Health, gain skill "Taunt" (aggros all enemies onto self, can be dismissed as an action, can be activated only once per combat encounter).
Requirements: Noble, Strength 7, Agility 5, Endurance 6, Courage 105
Executor -> Enforcer
Gain skill "War Cry" (whole party recovers number of energy points equal to twice the level of the user, enemies of levels lower than the enforcer's become intimidated and get a speed penalty equal to half the enforcer's level, can be activated once per a combat encounter)
Requirements: Noble, Strength 7, Agility 5, Confidence 105, Wit 100
Housekeeper -> Butler
Cleaning bonus is elevated to 100%, stationary jobs also allow the butler to tend to others' wounds (100% effect of a nurse occupation), can use "Mind Read".
Requirements: Agility 5, Magic Affinity 5, Loyalty 100
Geisha -> Succubus/Incubus
Escort/Prostitution bonus elevated to 100%, gains combat skill Allure (foe AOE spell, mana cost 10, all foes are afflicted with "Very Horny" status condition for the number of turns equal to half the user's magic affinity, can be used once per encounter)
Requirements: Noble, Beauty 90, Magic Affinity 7, Charm 105
Merchant -> Diplomat
Selling price increased by 50%, shops give discount on items equal to the highest of 15% and the slave's level while they are in the party (does not stack), gains combat skill "Bribe" (once per combat encounter for the price equal to half the chosen foe's slave price that foe turns on their allies and has a chance to join you after the battle if left unharmed; only works on enemies of levels lower than the diplomat's).
Requirements: Noble, Wit 105, Charm 100 Confidence 100, Courage 100
Nympho -> Depraved
+4 mana for sex, +100% to fucktoy earnings, no penalties for any sex actions, capable of initiating one extra sexual interaction when there are no sexual interactions left for the day, lust and arousal gains from sex are doubled, capable of orgasming in consecutive interaction counts.
Requirements: Commoner or below, Lewdness 120, Charm 50, Corage 50, Confidence 40 or below, Sex-Crazed, Pervert, Likes it Rough, Masochist.
Ranger -> Treasure Hunter
Item drop rate +100% (stackable), chance of the dropped equipment being enchanted +100% (stackable), hunting and forage bonus +100%, scouting bonus while in party. Can use Escape command.
Acquires "Scavanger" trait: the slave can choose an item from the mansion inventory, from the backpack, or from a market stall in any of the cities for a chance of drop of that particular item from any combat encounter in the Marsh or the Sea equal to [(scavenger's level)*35 + (the sum of levels of opponents faced in the encounter)*20)]/(the market price of the chosen item) percent).
Requirements: Noble, Agility 7, Endurance 5, Courage 100, Wit 105.
Tamer -> Bard
Twice the probability to remove the Uncivilized trait, occupation limitation on the ability to tame is removed, gains skill "Soothing Call" (party AOE spell, mana cost 30, effects persist the number of turns equal to half the caster's magic affinity, decreases stress at the rate of 10 points per round, regenerates health at the rate of 15% per round, can only be cast once per encounter).
Requirements: Noble, Agility 5, Magic Affinity 8, Confidence 100, Charm 105.
Trapper -> Hunter
First two escaping foes are guaranteed to be trapped and caught, foes that follow are trapped with probability of 50%, hunting bonus +100%, acquires trait "Stalker" (hunter can choose people of a certain race
as their target to gain a probability of either encountering them in combat or finding them among the bystanders in the Sea and the Marsh equal to (hunter's level)*3.5/(racial slave price modifier) percent).
Requirements: Noble, Strength 6, Agility 6, Wit 105.
Needless to say, if requirements for these are fulfilled only because of enchantments of worn equipment and it is taken off, or because of a consumable and its effect wears off, specialization bonuses revert to those of the previous specialization until the requirements are fulfilled again.
P.S. Harder encounters would be amazing too. Right now my master has 9 agility and 8 magical affinity (and no tattoos or lab augments), so I never have to be worried about anyone actually hitting me and I almost always solo bandit camps because of how stressful it is for my party members, which I feel like I should not be able to do and should not have to do respectively.
P.P.S. Main quest spoilers: imagine if Hade had a diplomat and an aggressor on him during the final encounter. That could turn pretty ugly pretty quickly.