QUICK ANSWER
There are five Theseus' Echoes. Interacting with their Axe Chalices awards Pierced Coin Charms and completing all five unlocks In the name of my kin.
What an Echo counts as
PowerPyx identifies the Echo interaction points as Axe Chalices. Each grants a Pierced Coin, and those rewards are included in the 30 Charms required for Superstitious.
The Echo sequence also has its own trophy, In the name of my kin, so completing all five advances two completion goals at once.
How to include them in a run
Follow the chronological collectible route instead of hunting them as a disconnected set. The chapter tracker preserves the resulting Charms, and missed Echoes can be revisited with Chapter Select.
Because the Echo rewards are regular Charms, they do not share the 165-point carry-over restriction.
Quick player questions
How many Theseus' Echoes are there?
Five.
Do their rewards count toward all Charms?
Yes. The Pierced Coins are included in the total of 30 Charms.
Sources
Primary game pages and specialist guides used for the facts on this page.
PowerPyxTrophy guide and roadmapPowerPyxAll Theseus' Echoes locations
