Here is the full list of all 33 Corpse Party (2021) achievements.
Completed Chapter 1.
Completed Chapter 2.
Completed Chapter 3.
Attained the true ending to Chapter 4.
Attained the alternate ending to Chapter 4.
Attained the true ending to Chapter 5.
Attained the alternate ending to Chapter 5.
Attained the "loop ending" to Chapter 5.
Completed Extra Chapters 1-10.
Completed Extra Chapters 11-16.
Attained all endings in Chapter 1.
Attained all endings in Chapter 2.
Attained all endings in Chapter 3.
Attained all endings in Chapter 4.
Attained all endings in Chapter 5.
Attained all endings in all story chapters.
Attained all endings in all Extra Chapters.
Found all name tags from Byakudan Senior High School.
Found all name tags from Tendo Senior High School.
Found all name tags from Amazaki West Senior Private School.
Found all name tags from Lexern Senior High School.
Found all name tags from Aizome Junior High School.
Found all name tags from Musashigawa Girls' Middle School.
Found all name tags from Musashigawa Girls' High School.
Found all name tags from Seisei Academy for Girls.
Found all name tags from Misato Municipal Brotherhood High.
Found all name tags from Hakuro #3 Junior High School.
Found all name tags from St. Maryanne University High School.
Found all name tags from Paulownia Academy High School.
Found all name tags from Distant Futures Elementary School.
Found all name tags from Shibagami Private Senior High School.
Found all name tags from every school.
Attained all endings and found every name tag.