Here is the full list of all 48 Heroland achievements.
...But I worked until the end, hooray!
Clear Chapter 1, "The Prince and the Part-Timer"
Clear Chapter 2, "Enter the Prettyboy Prince"
Clear Chapter 3, "Inspector Fortran: Case Closed"
Clear Chapter 4, "Quest Status: It's Complicated"
Clear Chapter 5, "False Friends"
Clear Chapter 6, "Of Manga and Monarchs"
Clear Chapter 7, "The Frozen Paths We Walk"
Clear Chapter 8, "Throw Wide the Gates!"
Clear Chapter 9, "Onward, to Our Dreams!"
Become besties with 18.
Become besties with Oak.
Become besties with Jason.
Become besties with Kotori.
Become besties with Otterman.
Become besties with Mel.
Become besties with Julia.
Become besties with Mana.
Become besties with Miranda.
Become besties with Philip.
Become besties with Fortran.
Become besties with Cobol.
Become besties with Linda.
Become besties with Chip.
Become besties with Chocola.
Become besties with Leda.
Become besties with Logo.
Become besties with Cee.
Become besties with Python.
Become besties with Vhoebe.
Become besties with everyone at Heroland.
Purchase all types of merch from the Item Shop.
Purchase all types of merch from the Blacksmith's.
Purchase all types of merch from the Plushie Emporium.
Use every type of recovery item.
Use every type of comic.
Use every type of capsule.
Use every type of hammer.
Use every type of sword.
Use every type of staff.
Use every type of tablet.
Complete the MonDex.
Collect all pieces of furniture.
Collect all plushies.
Collect all replicas.
Become besties with Apple.
Become besties with Delphi.
Become besties with Cherry.