We added in more achievements to After School Afterlife! You don't have to replay the game to get these achievements. Just open up the game and boot up your save file. With the exception of the post game and PSLE achievement, you should be able to get the rest retroactively.
A couple achievements cannot be gained on the same save file if you have already played past a certain point and missed the NPC encounter/interaction.
Also, if you'd like to support us, please drop us a review! We are currently one short from ten reviews (Steam does not count reviews from those who received steam keys for free). At ten reviews, Steam gives us an official score and that helps our game's visibility!