You just killed my dreams and pissed on their corpse...
Hoping for the Hat of Retcon? As soon as Harry makes it, it magically propagates through time and space on Harry’s head wherever and whenever he is/was, so Harry always wore a hat, in every universe, all the time.
I think perhaps more likely a magical device which aids in point to point teleportation. Harry has had significant interest in teleportation and sees how useful it is. Being able to grab an enemy and teleport them to the lakeshore to Alfred would be of tremendous benefit. Saves all the trouble of having to lure them there. I note nobody teleports to Demonreach, even Mab, it may be because it is over a significant body of water and magic is grounded by water, a signal degradation effect which might be fatal, an added protection of Demonreach perhaps. Embarrasing if only 20% of you arrives or it is all jumbled up.
Teleportation is also forbidden to Wizards perhaps because of the reasons set out above, so no one has made a magical artifact aiding in it. So a safe, reliable teleporter artifact which is Dresdens ultimate Hail Mary, and can be used by others.
It strikes me Harry would have mastered teleportation using Little Chicago, at least within the City if he still had it. Little Chicago would be out of commission if it was still around as Ethnui altered the Cityscape too much. Maybe Lea or Mab rescued it after all and will give it him back now it’s broken and he can keep it properly secure this time. Of course he now has the Za Guard to help him collect samples and plenty of space to make a Map Room as part of the Castle. His hand is much better as well. New Little Chicago?
Harry wouldn’t make a sword.
He would make a gun capable of doing the same.