Essentially, imagine a blade that was stuck between dimensions - between Void and Realspace. I'd imagine it would look ghostly and constantly be shimmering, seeming to be unaffected by gravity. Sounds like just another sword right? It would look to be so, until you started using it. You begin one swing with your Warframe, before the blade shimmers deeper into the void. Then - your Tenno would phase out of your Warframe, grab the blade, and then attack with it - looking much like (sigh) a Stand or perhaps the Wraith Stun Combo from Shadow of Mordor. Either way, after your Tenno uses it, it would be "pushed" further into realspace. Then, your Warframe would grab it, and... Well, it's a back and forth. A blade shared between Operator and Warframe.