Sylphy seems to get a lot more innocent/submissive/lusty/etc. at night, then gets really embarrassed about it the morning after. This time she ended up acting really cutesy and playful, which is totally at odds with the tough war princess persona she puts up in front of everyone else.
Could also be related to the blood moon mod for Minecraft, which follows the same pattern of one happening every seven days. Still neat to see the mechanic included in a manga like this.
That mod actually came out a full year after 7DTD already existed. And, as I said, there's a number of other things that are linked to it, including that achievement system and the way it gives a name to things (the descriptions, though? Those are totally being written by the god he's the apostle of, enjoying watching what he does and commenting on it). See:
https://steamcommunity.com/sharedfiles/filedetails/?id=2734081184 for that. There's also things like the specific look of several of the buildings, like the crafting bench, though the furnace IS straight out of minecraft and operates as such; the way the crafting menu looks and operates, including how it counts down the time of the craft before moving on to the next queued craft; the recipe book (done FOUR years before Minecraft! It was only added in 2017); how tools create a spreading crack in the thing being harvested until it suddenly poofs into the finished harvestable resource (curved tree into massive straight log); how splints almost immediately cure broken legs; the incredibly rapid growth time of player-planted crops vs. "wild-planted" crops in player-touched soil; there's more, but I'll leave it at that.
Yes, there IS minecraft elements too, like how he can just immediately harvest blocks, and how he actually gets the block back instead of bits like he would in 7DTD, but 7DTD functionality is actually far more prevalent; it's basically 7DTD but wherever there's a negative to make the player have to work for something that's too specific to its game world, it implements another game's method instead to make it easier on him. An example of that is how he removes areas of terrain with his shovel (they are NOT bounded to squares, he can actually manipulate the area being dug; squares are simply the most common), whereas in 7DTD he'd remove part of the voxel-based ground solid'durability until he finally take a weird chunk out and the terrain shifts to accomodate that removed section instead; another would be how a lot of things get stored as square blocks that wouldn't otherwise, like dirt, which would be a pile in 7DTD. Something that is NOT an example is actually the infinite water well, since they both have, or at least at one point had, that (as I recall they removed, or at least tried to remove, infinite water in 7DTD, but it was in the game for the longest time).
