I believe if I understand correctly what you say about the sandbox mechanic of the game, can be summarized as the following:
Sandox is NOT the core gameplay mechanic of this game but rather it allows the player to access different contents (or characters) in a non-linear fashion (as compared to the typical VN approach). For example, let say you have map, you you can go to place A to access contents with LI A, or place B to meet character B, in any order you like, event B might be locked behind event A, so you have to complete event A first, advance they day/time, go the place for event B (which was previously hidden), if you don't like character D, just don't go to place D and advance the day/time etc. More or less, sorry I am not good with words myself
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By the way, interesting and nice game, the renders is pretty solid for Honey Select. I never played it before but had kept watch on it. Will play when time permits. Well done and all the best, dude. Cheers.