Well, I don't really know where to start spoiler. Manga made up a lot of new things, which are good IMO. The way MC tweaking his storage to change the tragectory of weapons and making holes on the floors is very creative and exclusive for Manga (WN MC main weapons are swords and throwing balls)...
In Web Novel, he trained his gravity magic to the point that he "reduce weight" so he can swing the sword at fullest speed and then he "increase weight" before the impact.
With this method I think he can make any slash plausible, more or less.
Yeah, kinda true. The concept of gravity is the only knowledge from old world. Later in the story, there'll be some God-mythology reference but still not enough.
He won't try to sell food, not craft something from his old world knowledge. It's more like he will live his life to the fullest in...
Have you ever seen "King Gidora" meme, the 3-headed dragon from Godzilla?
At first, both of the heads are "silly". After the story progress, Illusia is still the "silly" one but the partner is become "fierce" one. 🤣🤣