Here is the full list of all 15 Hello Goodboy achievements.
Experience the ending of the Iko's journey
Experience the true ending of Iko's journey
Experience all of the season arc endings
Spend time and eat lunch with Brua
Get a friend for Brua and a hug for Porcupine
Choose Hedera's side and spend time by the lake
Choose Hachi's side and spend time in the forest
Spend time and eat satay with Ozzela
Find and return Ozzela's whetstone
Spend time and eat soto with Margaret
Unfreeze Panda by bringing her a bowl of soto
Help Hen & Goose
Do every good deed and get maximum amount of joypiece
Refuse to do every good deed and get minimal amount of joypiece
Repair all of the broken things in Kuruto