Can someone explain to me the function of sentences ending with “su,” and (what sounds like) “arisu” or “arinsu?”

I don't know if this belongs here, but——I recently embarked upon the journey of watching Overlord and noticed that Shalltear sometimes finishes her sentences with "arisu" or maybe "arinsu?" This got me thinking about how I also often notice that Gobta from TenSura ends most of his sentences with "su."

Is it something similar to how Kenshin ends most all of his dialogue with "gozaru," or what's going on?