As Captain JJ says, I'd use the historical as a starting point- it has to look the part if you're going to name it after a historical weapon. But of course, this is 40k, and plain weapons just don't fit in. We like ornate things for our elite soldiers- just look at the new Blood Angel and Grey Knight Thunder/Nemesis Force Hammers, completely covered in decorations.
What I would like to see is varying levels of decoration on the weapon, or at least different kinds
of decoration. A skull on one, a medallion on another, a purity seal on the third, etc. If every weapon is decorated the same (like your medallions on all three) then no matter how cool the decoration is, it becomes common and uninteresting.
Also, as much as I like the Ultras and the Agemo, a blank space on the weapon that can be used to affix decorations of our choosing would be cool. That way we can decorate it ourselves with purity seals, skulls, brass etch chapter badges, etc.
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