Remember that Vergil DOES NOT LIKE USING GUNS. Vergil considers guns "unworthy" of a true warrior. A good idea for an upgrade for Vergil would be a new powerful sword, or upgrade to his Demonic Abilities (or even an upgrade to the Devil Trigger.)
Do you really think I'm that stupid? *Walks into a door* Okay maybe I am that stupid...
To adapt with the RP, Renamon and Nera can practice with Reimu, Sanae and Yuyuko with the spiritual part, Meiling, Flandre and Sakuya with the physical part and Yukari and Reisen with the emotional parts
Have you ever crossed the line between sanity and madness? You would be amazed by what lies beyond the fog..
From the wiki here is a bit more on Dante's powers.
He is able to channel his power into various physical objects, ranging from his guns to the air itself. Dante can also hold his breath indefinitely, or perhaps even breathe underwater, as he can remain submerged for extended periods of time without taking damage or needing to surface for air. Additionally, Dante possesses great resistance to heat, as shown in Devil May Cry 4 when he casually sat on the flaming tail of Berial and came out with little more than a burnt coat. In the opening cutscene of the original Devil May Cry, he demonstrates telekinetic abilities, catching Trish's motorcycle in mid-flight before shooting it with Ebony and Ivory.
Maybe Dante in the Devourer Arc can get more powerful telekinetic abilities?
Also maybe his Devil Trigger (along with Vergil's) will become stronger and more "mature" because the Devil Trigger is still in it's infancy through Devil May Cry 3 (Story wise it is the first game in the series) and in Devil May Cry (which follows after Devil May Cry 3.) Meaning their Devil Trigger's will have them resemble their father more. As well as having enhanced powers.
Do you really think I'm that stupid? *Walks into a door* Okay maybe I am that stupid...
Hm..upgrades...For Mima, I would think something that could increase her magical potential overall, maybe being able to phase through walls?
For Hank, probably something that increases his agility, along with increasing his skills with weapons.
For Koishi, probably something that increases her stealth abilities, maybe revolving around increasing her subconsious manipulating abilities.
Question: Do villians apply to the whole upgrade thing?
Sometimes when you're driving down a road, a bug hits your windshield. It's ugly and unpleasant, but you just activate the wipers / cleaning fluid and it's gone in a few seconds. It's just part of driving down the road. You don't dwell on it, because that'd be silly. Bugs aren't worth the time.