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