You have learned "ku"

Complete the Prologue.

Collect a reward

Reach question 5 in normal mode

Locate and greet all Spirits in the Spirit World

Make it out of the Spirit World

Find and light all 8 types of carved Ancient Murals

Destroy 18 Plague Tethers

While in Spirit Form; step on a pressure plate, an unstable platform, and walk on water

Collect 50 Spirit Bloom

Cause the Wisp chirp 100 times

Destroy 8 Plague Tethers