If we're using them as nouns, otherwise no.

I don't believe it actually affects anything wikia-related in the long run (or affecting important stuff like strategy-forming during events).

For technicalities, "Kai Ni" would simply be official due to the fact that the game writes it as 改二, i.e. in kanji. There is also technically nothing wrong with Kai 2 because Japanese textbooks do match Arabic numerals with their kanji counterparts as well. Therefore, if you read "Kai 2" in Japanese, it's the same thing.

I'm in favor of Kai Ni just for keeping names in words (and that it's clearer that we mean "ni" not "two", even though I would still read Kai2 as Kai Ni, despite being American, since it's a Japanese ship/equip)

K2 is fine for abreviation

Guys, and Why we don't use Roman numbers? I, II, III, IV, V, and so on? The numbers are quite easy, and one can pronounce it as you want. Personally I would like to use Japanese Kanjis for the numeration, but no everybody speaks japanese. Nevertheless as XiaXueYi  says the arabic numbers and japanese numbers mean the same. And taking on account what MysticHrist  says too, Roman numbers are easy and short to write.

you mean like I-58 Kai II?

Roman numerals are interesting. I think they can work as well. Also, they look much cooler than the good ol' hindu-arabic.

So far we have:

• Kai Ni, to stay true to the actual Japanese

• Kai 2, for international use

• K2, same as above, and to save space

• 2nd remodel, for a literal translation

• Roman numerals, coz they're easier and look cool

Roman numerals are already assigned to Abyssal Equipment. Using the same set of numbering for user playable ships may end up confusing people.

Again my former point still stands, this is a Japanese game. Learn some Japanese and stop looking at compromises other than to save space. Besides it already appears that the retaining of use of Romaji is here to stay. If anything other than Romaji would be the literal use of Chinese/Japanese counting system such as 改二、改四、etc.

Yeah, I think @Crazy teitoku said it best.

I would add that "2nd remodel" works just as fine, but it is wordier.

kai ni is short, looks good, and rolls off the tongue better than kai 2. Kai ni all the way for me.

But Sr... The Abyssal Equipment uses the Prefix "Mk." and Imperial Metric System... There is no way that someone could get confused.

Nevertheless, I support you on the idea of use japanese kanjis on the numeration.