Greetings from Drillimation Systems.
We have gotten reports of complaints from players saying they cannot unlock the “Return to Ahoge Peninsula” achievement after clearing Arcade Mode with both characters and shot types in Chuhou Joutai, which unlocks the Extra Stage. Due to an error in the unlock criteria for the achievement, the achievement would not unlock even if you beat Arcade Mode with both characters and shot types. This glitch was discovered almost yesterday when we were adding a new feature to the game.
At the end of a regular game of Arcade Mode, even if you beat all stages, some achievements are unlocked based on what you did in the game. The way the achievement is unlocked is by checking if the values for if the game had been beaten with that character or shot type. However, since the boolean values are stored in .ini files (uses the proprietary .sav format) as real values, it can’t simply read them as bools. So, the bug just does that.
Fixing the glitch
If you have the Steam version, the patch will automatically download and your save data will not be affected.
You will need to download and install the latest version from the game’s itch.io page. Once you install the new version, you will need to follow the instructions for transferring save data, which can be found here.