I've Been Killing Slimes for 300 Years and Maxed Out My Level Novel Volume 15 is written by Kisetsu Morita with illustrations by Benio.

I've been killing slimes for 300 years, and my family has finally decided on my birthday! We didn’t have a date until now (mainly because I forgot it…), but my daughters are going to celebrate it with me this year, and I'm really, really excited! Later, I meet the goddess of fate (I can't be surprised anymore!), I help out a phantom thief (and my family grows), and I visit a strange land where there are no slimes! I'll share another short story from a drama CD at the end, so don't miss it!