Yea same, 2-3y for me, I only vaguely remembered about it too, I rechecked briefly early chapters to refresh on the few glimpses we had on high elf life for this arc, was surprised to find the higher spirit chapter so early yet nothing rly was said and nothing after (unless some higher creature...
Don't they become "high spirits" or smt? Like the water spirit in the early chapters, that one had a personality.
Can't exactly remember if they mentioned which type or if there is even a difference between the 2 (did normal elfs turn into them too, but small? or maybe smaller spirits could...
Man getting to read this work is somehow a pain in the butt currently (as if getting the jp dub wasnt a pain already) : the chapters are somehow out of order or missing right around where the anime ends, some chapters says they are "official" some are "billibilli" (which should be official, but...
for anyone else curious, looking at raws (14.2), seems they only went up to episode 7 of anime, altho without even finishing the very last part (it stoped before maou picked the guy to throw, unless it was planned to be different in manga)