Have anybody wondered why this game is called II.5 instead of II.V? I mean like, the 2 is written in Roman, so why isn't the 5? 

Which logo would you like more?

 

I like Donald !!!

Has anything ever been measured in Roman Numerals? 

The only place it uses roman numerals for the HD collections is the logo.

They've used numerals when spelling out the full name of the game. For example the opening to KHII. but as far as I am aware, it's poor practice or at least not common to designate fractions with numerals. You normally wouldn't do that. I think "II.5" works just fine. 

They did the same with I.5 But yeah, roman numerals are only used for whole numbers.

You know they did the same thing with I.5, right? That wasn't a "1", that was an "i". They use roman numerals for the main numbered titles, so they would naturally have the "one" and "two" in roman as opposed to digital. As for the "5" not being a "V", it's because it looks better. Can you imagine how weird "II.V" would look? The "5" is meant to symbolize that it's the story and a half. So it's more like Kingdom Hearts 1 1/2 and Kingdom Hearts 2 1/2. Point is, 5 looks better than V. It's much more stylish and varied this way.

because even KH2 the 2 in the title was II and in 1.5 too.

so you can say the roman is part of KH titles meanwhile ".5" is just for saying a better version of the original 

for the logo II.5 is fine, but for writing in the forum i prefer 2.5

Because Nomura.

It is like Isamu said they only use it for whole numbers.

Like FX-2 or FFXIII-2.

Because this is how they do it. They use special and attracting styles, exactly like 358/2 Days (Three Five Eight Days Over Two) instead of just giving a number with Days.

Probably to make it Unique, as well as following the Whole Number Rule. "II.5" is a bit more Eye-Catching than "2.5" on a front cover.

 

Roman Numerals have been consistent with Square-Enix in their History but for this, they have delved into the realm of English Numbers. Just like with Final Fantasy Direct Sequels.