s01 special-1 — Eris the Goblin Slayer

The special plot goes somewhere after the first meeting of Rudeus with his father, in the second season after the 16th or 17th episode

Cliff was introduced to Eris a little earlier here

there is even a dialogue about the flight

I guess Cliff will show up more than once and talk😅 they still make a demon hater out of him mmm)