Hey, I started as a broadsword user, but got annoyed by always having to change to the bow to hit enemies in the back row.
Tried playing just bow, but felt weak, then changed to magic, since you can hit both rows with most spells and started advancing the game pretty fast, it's good mp also can be increased and the speed it recovers too. Focus o WIT on multiples of 20 and the rest on INT, whenever you have enough for more 20 on WIT, reset stats and add those points.
I also had issues with the demon lord, but what worked was using the first thunder skill to stun, then using the third ice and fire skills, when she recovers, use the third thunder skill, it stuns too, then both second fire and ice skills too, use suck mp whenever needed, the status potions too, you can use the tentacle bind to combo her too, up it to lvl 3. And keep that rotation, buy all the potions you can use per fight and use them for MP and HP and you should be good to go after practicing a bit with spells. They are good because you can keep guarding while they hit, but the downside is there is a lot going on on the screen and sometimes you can't see anything, lol. Ah, the 1.0 build has a bug that the firewall doesn't disappear after using it, so the effect persists until you close the game, which sucks, but I hope the dev fix it, great game!