It would be great if the original theme for the sealed sword was kept in one of its five star counterparts. Normal damage and the charge attack should be able to inflict any random status effect. The 4* could look like the sealed sword but it quickly changes it's color to any of the assigned colors for status effects. The 5* could look like the body of the divine avenger and the grand faust but with a glow that changes color. The charge attack could be a bullet blade that causes random status effects.
This has been suggested before. I think it would be fun to use as long as you were soloing, or playing with friends who didn't mind if your charge attack accidentally nerfed what they were doing--i.e., lighting the baddies they were freezing on fire--but most players would avoid it. Unpredictability just isn't something a lot of people are going to value in tier 3. Also, if, say, the blade regularly cycled colors (statuses) so that you had some degree of active control over the status effect of the charge attack, I bet you would have players howling that the sword was overpowered--after all, it would be a glacius/combuster/GF/etc. all rolled into one.