Hornsent

Speak to the Hornsent at the Three-Path CrossGrace

Speak to Hornsent at Highroad CrossGrace after the Rellana, Twin Moon Knight in Castle EnsisRegion

(Optional) Give Scorpion Stew to Hornsent at Three-Path CrossGrace

Explore Scadu AltusRegion, and after the shattering, return to speak with Leda and Hornsent at Highroad CrossGrace

Tell Leda to pick either Thiollier or Hornsent, it does not matter either way

Head to Shadow KeepDungeon and defeat the Golden Hippopotamus

Go through the Keep until you come to the main plaza of burning boats, at the top of the stairs, choose to help the Hornsent

Later, during Messmer's boss fight, summon the Hornsent inside the arena and speak to him afterwards

The Hornsent will later invade you in Ancient Ruins of RauhRegion, and this is the end of his quest