I'm surprised it took CR like a month to post an English article about this. The story was making its rounds in Japan last month because that was when the report was released on the investigation into his suicide, which was over 3 years ago.
There are a few interesting points to be made. First of all, overwork is not exclusive to the anime industry, it's part of Japanese work culture in general. Not something which has an easy solution, and I don't think the government is interested in doing much to change it.
Secondly, with regards to the "production runner" job in particular. It's a job which doesn't get much attention or credit beyond the production phase because it's not really a creative role and as such there isn't much reason for fans to care about it, but it's a vital one which can be extremely stressful and involves an insane workload.
A production runner is assigned to specific episodes of a series, where they're in charge of making sure everything from the start of pre-production to the delivery of the final master is done on time and to maintain the schedule and double check everything. They monitor the schedule for each step of the process, ensure that materials are completed and delivered to the right people at each step of the way, they double check all materials at every step to make sure nothing is missed out, count the pages, check to make sure people didn't forget to do stuff, remind people if they did, etc.
They might also be required to assist with things which no one else is free to do, like prepare filler text for on-screen documents and notes, or create the text from scratch, sometimes if they want the text in another language (usually English) but the show doesn't have a specialized translator on board, they're tasked with getting the text done (now you know why Google Translate crap shows up in some shows!). If Person A needs something from Person B but has no time to get it himself, the production runner could also be tasked with being an inbetween. It's a thankless job which requires full attention at all times and a well rounded understanding of everyone else's job. Screwing up could mess up the entire production line.
Sounds like a terrible job. So why do people do it since it doesn't even have artistic credibility like animators enjoy at least? Because it's the ultimate gateway to actually running something in the anime industry. Production runners can get promoted into various positions when their abilities are recognized, and they do a ton of networking as well. People who started out at various studios as production runners have went on to become directors, designers, writers, and most importantly producers who run and manage their own studios. If they don't die first.