I mean, I understand he had no way of doing his revenge right away and the only way to get stronger is to heal (and receive skills and levels in the process) people for the princess - but he could still do all of this WITHOUT going through unpleasant experience, simply by agreeing to work instead of acting afraid and refusing. He WILLINGFULLY put himself through all of this, only because he worried that his desire for revenge might die out.
The only thing he does to his revenge target is just breaking fingers few times, several bruises with external wounds, following with rape (with a help of red-hot metal). And to make matters worse, the latter part (rape) is almost completely skipped, barely any description! Even the first part of the revenge is barely described!
Just remember the School Arc – ugh, it's literally the worst arc of the novel and it shows all its main flaws clearly... Useless (bland) characters, Rudeus' way of thinking, childish interactions, unnecessary fanservice – you name it!
P.S. My review ended up being small, since I had been reading this novel a while ago, but hopefully I've managed to describe my overall impression of it. I felt like this novel deserved more negative reviews...
The modern world got swarmed by beings from Otherwold, demons, led by the so-called Demon King. The god chose 7 people and granted them power to save the world – and so they did. Due to the influence of the demons and the war as a whole, humanity came to know the existence of magic and ESP (extrasensory perception, espers and such, you know).
There are some suspicions around Earl Terejia and Priest Faris – and the way the seem to know something about her reincarnation – but it's all glanced over for whatever reason.
I don't really like the main lead, though, – he appeared out of nowhere and immediately started to have some sort of the feelings for the main character; and main character in turn started to behave like a girl from a typical shoujo: being flustered and allowing him to stick with her. He, in fact, looks like an obsessive man who wants to control our heroine – yeah, this kind of male lead.