Update: I figured it out. I'll post the solution here in case anyone else wants to do the same thing.
So first of all, that message at the top of the screen is called the 'battle log'.
First, go to Yanfly's BattleEngineCore plugin and find the 'startAction' function for the battle log. In that function, add the line "this.opacity=255". This will tell it to draw the (invisible) window for the battle log, which is created by windows.js.
Go to rpg_windows.js and find the Window_Battlelog section. Notice that it's already being drawn, it just has its opacity initialized to 0. Go to the function 'performActionEnd' and add a line at the end of it that says "this.opacity=0". Finally, remove the rectangle that the game normally draws by going to the function "backPaintOpacity" and telling it to return 0.
In my picture, I've also changed the width of the window to half its usual length in the initialization function, so it doesn't take up the whole screen. I might try modifying it further so that it grows or shrinks depending on the amount of text it needs to draw, but I'm not sure which looks better at the moment. Anyway, you can consider this issue resolved.
