His "loneliness" is a universal emotion I believe everyone has felt in their lifetime, at least at some point. While I'm not like Nacchan in a sense that I personally enjoy what I do right now---and it's the only thing I can imagine myself capable of doing so ig it's appropriate to say it's my dream job---I also still tend to envy other people, people like Issei who get to live a relatively carefree life, people in fields that just earn more, people who have more time despite having a job, people who have the skills/talent I wish I had or people who are just so damn good at what they do. And let's face it, some jobs just look more fun, regardless of what you're passionate about.
I still don't know how to navigate through such emotions (please don't reply "learn to be contented bs," that's a lot easier said than done) but I'm curious how the author will portray it in the MC's case.
What I know for sure is: jobs, in general, suck... and I'll always blame the capitalist system. The need to always grind without any assurance of any actual payoff.