NHK is a really fun anime. It can be pretty funny at times, but like you said it can be darkly serious and deals with some very heavy topics, especially for those in Japan, which being a NEET or Hikikomori is actual a real lifestyle that is all to common. The different things that happen like getting sucked into online game trying to make money as a goldfarmer, though the pyramid scheme and island "get-away" end up going to some very serious places, more the island get-away, but even the pyramid scheme is dangerous. I watched it on Netflix, don't know if it's still around or not, they tend to cycle their anime series more frequently than I'd like, namely that they don't keep things, but cycle them. So the library never grows, just always changes.