Thanks so much for playing! And for the comment! ✨
Firstly, there is no NG+ in LesbiAnts (though there is a cheat code you can put in that lets you play the game with every ability and upgrade). You also unlock the Gauntlet for beating the game, however, which is a boss rush that gives you a special set of art scenes for completing it, as well as unlocking the Gallery of all the game's art.
Second, the warning for data overwriting is there because I didn't use multiple save files in LesbiAnts as a way to make sure your "ANT-chievements" were carried over from new game to new game. It's basically just keeping the unlock data in the 3rd save file and warning that overwriting with a new end-game save could compromise that data. If I were to revisit the game (again), swapping out for a multi-file save would probably go on the list of changes now that I have a better handle on how it works. Sorry for the confusion!