Had they wanted to blow her out of the water, it would have been much easier then the explorative fleets encounter. The Yamato is terrifying enough prospect for the Ryujin, but it was with an escort of a light cruiser and five destroyers. Shouta is a man of pride, as a result, he's not taking the situation too well.

I want to make the chapters longer as well, but that also puts a  lot of pressure on me. I'm not very good at segmented writing, typically I write a whole chapter in one go, then edit it.

Yes I've read it plus more. More recently which I will share below.

Yes Ryujin woman are anywhere between 120 to 170 feet tall, with 150 as an average for adults.  Your right I did get the perception wrong on the bullet size, at the time i had been doing some other calculations and it got mixed in there.  However Oni fall under a larger scale then the Ryujin woman.

The ships themselves were fully armed before the operation, so it will be a while before thier out of ammo. Each gun had a life of about 500 to 700 shots and each gun would have had 120 ammo, with the ability to shoots 5 to 10 rounds a minute. Note these were seasoned battleships near the end of the war and also shooting faster results in more wear on the barrels. Speaking of ammo, due to the mission and lack of any air cover the destroyers most likely had an excess supply of incendiary shrapnel rounds made for anti aircraft. They might produce similar effects of a mini shotgun to the Oni. They rely on fuses which detonate by time delay which are manually set by the loader. As for the regular shot, what was common by the end of the war was most likely solid steel shot, or hardened tip sabot in Japanese munitions. So likely the destroyers in Operation Ten Go would have been armed with them.

The explosive shells Quote:

"The earliest naval and anti-tank shells had to withstand the extreme shock of punching through armour plate. Shells designed for this purpose sometimes had a greatly strengthened case with a small bursting charge, and sometimes were solid metal, i.e. shot. In either case, they almost always had a specially hardened and shaped nose to facilitate penetration. This resulted in armour-piercing (AP) projectiles.

A further refinement of such designs improved penetration by adding a softer metal cap to the penetrating nose giving armour-piercing, capped (APC) design. The softer cap dampens the initial shock that would otherwise shatter the round. The best profile for the cap is not the most aerodynamic; this can be remedied by adding a further hollow cap of suitable shape: APCBC (APC + ballistic cap).^[12]

AP shells with a bursting charge were sometimes distinguished by appending the suffix "HE". At the beginning of the Second World War, solid shot AP projectiles were common. As the war progressed, ordnance design evolved so that APHE became the more common design approach for anti-tank shells of 75 mm caliber and larger, and more common in naval shell design as well. In modern ordnance, most full caliber AP shells are APHE designs."

Here's some info "Japan 12.7 cm/50 (5") 3rd Year Type"

Also I thought I should mention that in 1943 the destroyers which would play a part in Operation Ten Go had their guns upgraded from 127mm to 130mm 50 caliber guns. Also the claims of armor penetration of four feet come from a cited Japanese test which was done, but it was not substantiated.

As for adjusting ammo, the guns fired bag ammunition and used a Welin breech-block, must often black powder charges. So adjusting ammo is possible.

The only one which did not use manual charges was an ASW Explosive shell which used propellant. But it could only pierce 1 inch of steel, and had a APHE flat head designed to explode on impact. "This might be effective, but I'm unsure if and how many they had aboard for Operation Ten Go

Likely the amount of shot able to be used will play a more important role in taking down a giant, since unless bone gets in the way, they will likely pass straight through.

 Thank you for correcting me about the perspective. That was a brain fart I wrote there.