Here is the full list of all 29 Onigo Hunter achievements.
Watched the opening.
Strengthened the Energy Alchemy Device.
Opened the door to the ruins with one's own power.
Became victorious in the fight with the butler.
Sealed away Kanai.
Defeated the alter ego of Kanai.
Successfully captured an Onigo for the first time.
Successfully captured an Onigo 30 times.
Successfully captured an Onigo 100 times.
Successfully captured an Onigo 300 times.
Used fortification for the first time.
Used fortification 10 times.
Used fortification 60 times.
Used fortification 100 times.
Raised the hunter rank to D.
Raised the hunter rank to C.
Raised the hunter rank to B.
Raised the hunter rank to A.
Raised the hunter rank to S.
Raised the hunter rank to SS.
Raised the hunter rank to SSS.
Completed 20% of the Catalog.
Completed 50% of the Catalog.
Completed 100% of the Catalog.
Completed 5 requests.
Completed 30 requests.
Completed 100 requests.
Harvested from a magic plant pot for the first time.
Harvested from a magic plant pot 20 times.