In my initial reply, I gave my entire knowledge of what video editors can do so I should be asking you for advice about video editing 
Being drawn/painted by an invisible hand (or a visible hand) is very possible using animation in krita.
Some examples:
Paint in haste, erase at leisure
https://forum.kde.org/viewtopic.php?f=276&t=161086
The ‘invisible hand’ painting effect is done with hand painted animated transparency masks. It’s a technically simple process but it takes a lot of time and manual effort.
For ‘wipe’ types of reveal/fade effects, you can construct animated transparency masks that can be reused in different projects.
This is something I’ve been playing with but haven’t got around to finalising or posting yet. (There are some interesting problems that need to be invesigated.):
I’d be happy to give you that collection of animated wipe transparency masks if they’ll be of any use to you but you’d then have to learn how to use them.
None of what you want to do is technically difficult but it does need learning and the ‘hand painted’ effects can take a long time.
You don’t need animated transparency masks to make simple entire frame fade in/out effects because you can use opacity keyframes on an animated paint layer.
I suggest that you start experimenting with animation in krita:
Animation with Krita — Krita Manual 5.2.0 documentation
Animation Curves Docker — Krita Manual 5.2.0 documentation
You can create a new topic for help and advice with any particular aspect of it all.
Good luck with it all and do show us what you make with it