I don't know if anyone will see this post now, in 2021, but I found it through Google so you might, too! Thus, here's my personal trick for this game~
Pretty early on, you'll get access to both Heal and Invigorate spells. Get these, they're both critical. This path involves a LOT of combat.. as much as you want, in fact, for your hero protagonist.
It's actually quite simple, What Invigorate does is, for 5 mana, you inflict some stress on someone in your team, of your choice, including captives, and will restore 50% of your max Energy. So, buy some rope, even one will do. Save your game, obviously, and go out. Fight, capture someone. They're an Energy battery now! Go out, fight more, gain exp, level up. Exercise "aggressive affection" on bandits you don't capture; at least you're not killing them, right?? And you need that mana! Heal and Invigorate.
Oh, you went back to the mansion to train and save, and it dropped off your captive? That's fine. You can get more. In fact.. the REAL way this shines is if you've also unlocked Sebastian.
Sell him your untrained captives. Yeah, you'll take a reputation hit but you'll get money and Upgrade Points. Sweet, sweet Upgrade Points. And the money, well, you won't get much from loser bandits around Winborn but if you go ->Outskirts->Plains->Big Sea you can capture some free-range Scylla and Nereids and they are worth hundreds of gold each, with Sebastian. If your Reputation with a city tanks, just go wander around outside that city and beat up bandits who are Harassing locals.
See how this works? You have infinite Energy as long as you have people to use Invigorate on. Gear up your slaver, level them, max out their stats, keep fighting. As much money and upgrade points as you could ever want, without advancing the days counter. Then, when you're as powerful as you want, proceed at the pace you like. Get new slaves, train them, acquire the special named characters, etc etc, the world's your oyster~
The only trick is getting strong enough to actually win all these fights, which is a hump to overcome early on. Get your Agility up, it's super important, it governs hitting and dodging and lets you use swords. Upgrade your armor, level up, buy your skills in the Mansion, dominate battles~ Eventually you'll be wading solo through those ten-bandit forts, shrugging off a hail of strikes while you put them down one by one ^^ I just wish there were AOE attacks... Strive: Conquest is great for that!
Good luck everyone, and have fun ♥