One Weapon Build: Submarine
If you can stack up the Submarine's Damage and casting speed, it can carry as both your source of offense and defense!
This is due to its effect, "Gain Shield equal to this item's Damage.". When you paired with Shipwreck, it can become an absolute monster.
Note that Kripp Enchanted it with Fiery but it wasn't really that impactful to the overall run.
Silencer is a classic choice for any one-weapon build, simultaneously boosting its Damage and Cooldown. It jumps up by 10% for each rarity, so make upgrading a priority. This will be your one non-Aquatic item.
Silencer
The Shipwreck is your second most important item after your Submarine - if you don't find it, scaling your build will be difficult.
Shipwreck
On the opposite side of your Submarine (the right being the Silencer) is the Captain's Wheel.
The Captains Wheel and the Submarine feed into each other since the Captain's Wheel Hastes it and then gets activated whenever the Submarine casts in return.
As an Aquatic item, it will also benefit from Shipwreck's Multicast.
Captain's Wheel
In your last Small slot is Clamera, a generally good item for Vanessa that is still solid after its own nerfs.
With the Haste from Captain's Wheel and the Aquatic Multicast from Shipwreck, it's your main source of crowd control to buy your Submarine time to ramp up.
Clamera