There's some minor differences with the official light novel but the what's going on here is that
Their village is made up of the descendants of this legendary kingdom built inside of a labyrinth that the MC mentions every now and again. The head hunter here is descended from their knight captain, with all of their spirit techniques passed down, and the medicine woman their head mage, who inherited all of their magical knowledge. The village head, the MC's adoptive father, is the descendant of the king and received all of their taming skills. Like they said in this chapter, they are testing Rent and Lorraine because they intend to pass all those techniques and knowledge on to them after telling them about their village's secret. That's why I said before that the way the manga rewrites Rent and Lorraine so they're less chill about their relationship and being mistaken as a married couple doesn't make sense, since this is part of bringing Lorraine into the family and sharing their secrets. The village is fine, btw. That's just Rent and Lorraine's misunderstanding.
There's 3 really. physical energy, magical energy, and divine energy. There's specific applications or things that are used kind of like an energy pool, vampire weapons use their blood to powerup, but it's really just the three that Rent uses. What the old man is doing here is just more advance applications of the same energy Rent was using to make his sword swings hit harder in the beginning when he was just a skeleton. He just knows how to use it better, hence why he's talking about how it's time to teach it to Rent.
Ok cool training arc and all, but why did you have to set fire(?) to the village(?) to do that?
Also I'm calling that 'the end of hatohara' is some bullshit that's not going to actually be the end of anything except semantically(like they're gonna rename the village to harahato or something).