Kaga was a smaller aircraft carrier than Akagi if I remember, right? But did she come first in construction and deployment? If so does that make her the elder sister even though she's a smaller ship? (Sorry, thinking almost entirely in normal warship ideas here)

Animefan162a said:

Kaga was a smaller aircraft carrier than Akagi if I remember, right? But did she come first in construction and deployment? If so does that make her the elder sister even though she's a smaller ship? (Sorry, thinking almost entirely in normal warship ideas here)

I think so. After all, both of them are classified as Kaga class carrier.

Akagi was laid down as an Amagi-class battlecruiser and converted to a carrier, launching as Japan's second on April 22, 1925.

Kaga was launched as a Tosa-class battleship on November 17, 1921 but was converted and redesignated as Japan's third carrier on March 31, 1928; originally this was planned to be done to the Amagi, which was damaged beyond repair in an earthquake.

Animefan162a said:

If so does that make her the elder sister even though she's a smaller ship? (Sorry, thinking almost entirely in normal warship ideas here)

A little late, but I can provide an answer from nautical lore which you or anyone else may find interesting.

Elder Cousin, actually.
Sister ships are ships in the same class.
Cousin ships are ships that are either of the same direct class (US Naval Ship Designation Code of the same 'Fleet Era' [Age of Sail, Age Of Steel, Pre-Dreadnought, Post-Dreadnought, Post-1975, and 21st Century are all of them so far) or belong to the same direct development tree (Almost any American Military ship of the same ship type is like this. In this way, Kaga and Nagato are also cousins.)
Also worthy of mention are Half-Siblings, which would be two ship classes that came from the same planning stages. This would be like the Iowa-class and the Montana-class, off the top of my head.

See, the Essex-class USS Lexington (CV-16) is a sister ship of the USS Essex itself (CV-9), yet a cousin to the later Midway-class Midway (CV-41) and even the much more recent USS Gerald R. Ford (CV78), albeit distantly (via Development Tree).

Interestingly, albeit related only remotely to this subject, the USS Lexington (CV-14) is the daughter ship of the USS Lexington (CV-2).
Any ship that carries the name of a previous ship, directly as a namesake directly, is the 'daughter' of the namesake.
(Unless you're speaking of a Russian ship, then it's a 'son'.)

This certainly has certain interesting implications for certain ship girls.
Such as the 'Zekamashi' loli that runs around in a (clearly visible) thong.
Yeah, she's a mother.
Oh, and the 'Nanodesu' loli and her sister?
They're grandmothers.
In fact, many of the Cruiser and lower KanColle ships qualify as parents. Even some of the Battleships.
This can certainly give rise to odd situations given the recent marriage function...

Edit:... I keep forgetting the 'No Bump' checkbox...