Yall should read "Veldora's Slime Observation Diary"
Its basically extras that come at the end of each manga volume tankobon.
Its in novel form and basically depicts Veldora's POV and impressions on the plot while hes in Rimuru's stomach.
Hes able to see everything thats going on, and really changes his perspective on everything hes ever known.
Before, he only wreaked havoc everywhere, but seeing Rimuru interact with everyone and working together to build Tempest has Veldora yearning for those connections too.
It gets better after Rimuru absorbs Ifrit, usually Ifrit would have been broken down into magicules but Veldora intervened and brought Ifrit to where he was and now has a playmate
They play games together, train together, and eventually truly become friends.