It was serialized online between 2013 and 2016 on the user-generated novel publishing website ShÅsetsuka ni NarÅ.
Diablo, on the other hand, probably doesn't care too much, especially since he has found Rimuru to serve and dedicate his life to.
Glow-in-the-dark craft paint is available at most craft stores as well as in the crafting section of many major stores.