https://hostednovel.com/20164/novel/reincarnation-of-the-strongest-sword-god-side-stories/rssgss-chapter-2.0001 new series

He mentions them once near the end of the novel, they live in the upper zone presumably

There's a sequel on hostednovel https://hostednovel.com/20164/novel/reincarnation-of-the-strongest-sword-god-side-stories/rssgss-chapter-2.0001

There's a sequel on hostednovel called alternate ending. The author writes it for fun, if you wanna read it