The MC is the annoying type, he's super OP but so weak mentally.

When he was kid he made some promise with his childhood friend (Aria) that they will be together after that because she can use magic she goes with the hero party to deal with the demon lord and when she's back the MC found her kissing the hero. He run from home while crying leaving behind his little sister, and whats more annoying is that he leaves behind a letter for the b*tch (that he wish her happiness with the hero) and didn't bother to tell his sister.

Well after that he goes to the forest for 2 years and become OP, on the way back he will help a some elves and he will fall in love with one of them, he stayed together with them for some time finally he decided to confess but she turned him down and he started again running and crying for days like a little b*tch. After that the story goes like any others harem Japanese novel saving girls and they fall for him while still thinking about his childhood friend he even meet the elve girl for second time and she wanted to be with him of course our MC can't No.

To see the MC grow some balls you will need to wait until the last chapters when he will go to the king city were the hero party live, he will start searching for the childhood friend and when he find her she will turn him down for the second time telling him that promise they were only kids and that she fall for the hero (well I can understand her I mean between the cool hero who fight demons and save the world and a kid who knew nothing just sitting at home any girl will choose the hero) well now everyone knew what will happen next our MC shut himself inside his room for 5 days crying and regretting his useless past only after that he will mature a little and goes to apologize to his harem member after that some action will happen and the MC will show his strength, everyone will be shocked and he will look att his childhood friend with cold eyes that he no longer love her and bla bla bla

It's an interesting story about how an ordinary person that became OP fares in a world where there are possibly 'Summoned Heroes From Another World'.

The novel alludes to the Hero that takes away Aria, his first love, being from another world (Japan). It can be seen later on in the book that there are more of either 'reincarnated' or 'summoned' people due to the appearance of 'Shampoo' and 'Soap'.

Moving onto the main character, Wazu, his reactions may seem to be that of an immature child, but that's because he is one. He's not 'reincarnated', nor is he 'summoned'. That is, he doesn't have 2 lifetimes of experience nor is he forced to mature quickly. It is normal for him to be depressed and run away from something that frightens or depresses him. Maybe not to an extent that he would run off to a mountain full of S-ranked monster, but it's a fantasy novel; it's probably the only way to explain his bullsh*t OP power that derives from goddesses.

His maturing through the novel can be relatable if we also lived in a fantasy world, but it isn't, to be honest.

As of Chapter 98, we don't really see any mentions of Aria, except for when they meet at the guild. And even then, she hesitates to ask whether or not the MC is the same person she knows. In all honesty, I hope Wazu moves on from Aria and the girls who he likes after her meet up with him.

Why? Because it would be great to see misunderstandings clear up. Of course, the plot is sort-of built on misunderstandings and comedy ensues to it, but hey, all things have to end at some time. The girls are so in love with him that they would travel and follow his trail just in order to clear up misunderstandings and become his harem.

tl;dr
It's basically about our MC, Wazu, maturing after he gains a OP power. Comedy ensues due to hilarious misunderstandings. The dark part of the story is only a small part of the story.