To paraphrase the late Sir Terry Pratchett, A sword is for the messy business of dynastic surgery.
OK, I just really wanted to say that.
You have a number of things you need to consider when constructing a sword of any size.
Fighting style is chief among them. Your fighting style shapes the blade, so to speak. A Style in which your opponents are going to be wearing minimal armor and is geared toward stabbing, you use a rapier or an epee. You want something that can be moved very quickly and thrust into your opponents squishy bits. This style needs a lightweight, long, thin blade with a very sharp point. It's not going to have a focus on a sharp edge because you are stabbing, not slashing.
A Style that focuses on men in armor is going to need a much heavier blade in order to punch through. This blade may be single or double edged and would rely on a broad swing or a two handed thrust with the point.
Yet another style that relies on slashing cuts to cut armor away and damage mounts and stuff will look more like a samurai sword. Single edged and very sharp.
So why would you need a 7 foot long samurai sword or a Cloudbuster bastard sword from Final Fantasy 7? Let's just roll with it. Something like Cloud's sword I could imagine being a useful tool to take out mounted opponents and to smash it's way through things That means it needs Mass, and lots of it. That creates a problem for you, since you are trying to get it down to a realistic weight. Reducing the mass means less energy at the tip of the sword. There are better weapons for that, called pikes and halberds. They aren't as sexy, but they work.
The 7 foot samurai sword runs into the same problem. There are better ways to deal with your enemy if you want to kill them from a moderate distance.
This is all just to point out some basics. If you are not going to invoke Handwavium or the "Rule of Cool", over-size swords don't make a lot of sense.
Now we come to your sword design. It looks like something that would be used to smash your opponent, kind of like Cloud's blade. It's not going to lend itself to a finesse kind of style. If you want it to have a hollow core to save weight, you need to design it so that the sharpness of the edge focuses the energy of the swing into the smallest possible area. In addition, you might want your style to focus on hitting joints. It's dumb to just go after the torso of a man in plate mail with a slashing attack. Also, if it's hollow, it's going to be fragile. Once the integrity of a side is compromised, the whole darn thing is going to crumple around it. So your guy is going to have a style that focuses more on dodging attacks rather than using his sword to outright block an attack.
As Always, the fighting style must match the blade. You are just coming at the problem backwards. You can excuse some of the problems of a giant blade with Handwavium or Magic, but if you ignore the style of fighting, you end up with silliness.
something I thought of that might be helpful.
Handle design is also critical in your sword's design. A Katana has a long handle and is designed to be used two handed. From my (very brief, and a long time ago) exposure to kendo, The grip is supposed to be loose right under the hand guard with one hand. The other hand is at the bottom of the grip, with the pinkie actually under the grip. This hand grips the sword firmly. This gives you a fulcrum at the hand guard so that strikes are faster and more controlled than what you could manage with one hand or with both hands gripping the sword handle right on top of each other. combine this with the old kinetic energy = mass times velocity squared. The energy at the tip of the weapon is greater if you can get the sword moving quickly. A one handed grip on an oversized sword is not going to work especially well unless the guy wielding it has arms like a cross between Dwayne "the Rock" Johnson and Popeye.