Sure thing-- that part is actually really, really easy, except for the part where it interacts with your script. (I can't predict how that will work out, I'm afraid. But this method might just take care of it...)
Here, I'm assuming that the script still allows for playing User Animations with skills. If not, well, you'll need to either find a different script, or edit that one.
But anyway.
First, create an Animation graphic the way that I described above-- create a .png graphic that is 960x a multiple of 192 pixels in size, that is entirely blank. (By blank I do not mean white-- I mean transparent. This is why it needs to be a .png file, and this means that you'll need to use a graphics program that supports this. Photoshop does this, but so do the free-and-much-smaller Graphics Gale and Paint.net, or the larger-but-still free Gimp, so you have some options here. You'll want to have some kind of decent paint program available to you. Ignore MS Paint entirely.)
Next, copy all of those graphics that you want to use over as cells. You'll have an easier time if they're precisely centered, so snap on a grid. Import this graphics file into the Animations folder of your game.
Okay, now for the fun part.
Create an animation for the skill being used. Select your huge Luffy image as the cells to be used for this one. Make sure to select Luffy (or whichever character you want to use) as the battler to use in the background-- it'll make your work easier.
Frame one, pick a starting pose for Luffy. It's kind of handy if this one is exactly the same as a frame of his normal standing pose, but it's not necessary. Make a cell of that image, and change that image's transparency to Normal instead of Add. (You get to the menu that lets you do that by right-clicking the cell.)
Move that cell around until it is completely superimposed over the normal battler image for Luffy.
Now, go to the top-right section of the Animation options-- the place where you'll add things like Sound Effects and Screen Flashes.
But in this case, we're going to pick the option Hide Target. Have that happen in Frame One, and the duration? Is the
entire length of the Animation.
From here, create your animation in the normal way-- go through, frame by frame, and use all those lovely images you have to make your Gum-Gum Grand Piano Crusher, or whatever. Make sure to set the transparency to Normal for all the frames of the character, though, or it's going to look off when it's done.
If you want to show the character actually charging up to the enemy and hitting them, and I'm sure that you will, there's another step: Create the Target Animation. You'll use the same Animation graphics, and set the cells to Normal Transparency, once again, but you won't need to center the starting graphics around the center battler, or use Hide Target unless you want to make the target of the attack vanish.
If you do this, you should probably make Luffy jump out of his own frame in the User Animation-- that is, have the image of Luffy run or jump a short distance, and then have another 16 or 40 or whatever frames of absolutely nothing, with the Hide Target effect still going.
And now all you do is go to the Skills tab, pick out your skill, and set the User Animation and Target Animation to whatever you like.
Also, you can do both sides of this equation with
any and all weapons, meaning that you can do a normal Attack where Luffy jumps on top of someone and pounds them-- you'll just need to make sure that all of the weapons that Luffy might use are Luffy-only weapons, or it'd get pretty surreal.
Then again... One Piece. Perhaps you'll want a sword that turns the user into Zoro for the duration of their attack...?
