Made in Abyss Vol 6

Made in Abyss Vol 6 by Akihito Tsukushi. A Fantasy manga rated Older Teen, published in English by Seven Seas.

The Abyss is an enormous, unexplored chasm full of strange creatures and priceless relics, and the deeper you go, the harder it is to return. Orphan Riko dreams of following her legendary mother into its depths, and when she finds a mysterious robot boy named Reg, the two set off on a descent that will test everything they have.