Midweek discussions - Volumes that withstood Time

What are your favourite Light Novels that are at least 10 years old?

I have recently read "I Saved Too Many Girls and Caused the Apocalypse vol 1" and to my surprise it started publishing in 2011. Most novels I read are fresh, with new volumes constantly being pumped out. It drowns out discussions about stories that are older but still worth the read.