There are some methods of romanizing Japanese, the most common ones are Hepburn and Nihonshiki. In short, Hepburn is based on how we pronounce Japanese. Nihonshiki is based on how we type Japanese into an IME system.
The method used in osu! needs to be consistent, it just leads to inconsistency in metadeta of beatmaps and stupid unranks otherwise. I think Hepburn romanization is the best one since it's closest to what we do in osu! now.
However, long vowels such as "おう" "うう" should be romanized into "ou" "uu" instead of "o" "u", since we cannot use a macron in a non-unicode field. It has already taken root in osu! so you probably find it more natural. And using "o" "u" also makes us unable to tell the difference between 2 different words which have the same romaji, for example "Yuka" and "Yuuka". And "ou" "uu" show their actual pronunciation so they help you know how to pronounce them correctly.
For example:
O Touhou
X Toho
O Shippuuden
X Shippuden
Also there are many variants of Hepburn romanization. The two most common styles are Traditional Hepburn and Modified Hepburn. They're basically the same but different in some respects. See Wikipedia for their detailed features. As you can see in osu, we romanize particles "を" "へ" "は" into "o" "e" "wa" so modified Hepburn seems closer to what we have in osu!
tl;dr - Refer to Hepburn romanization when you romanize Japanese. Long vowels such as "おう" "うう" are romanized into "ou" "uu" because we cannot use a macron in a non-unicode field.
See also:
[Rule] Romanisation of Chinese, Japanese and Korean titles
Any suggestion?
The method used in osu! needs to be consistent, it just leads to inconsistency in metadeta of beatmaps and stupid unranks otherwise. I think Hepburn romanization is the best one since it's closest to what we do in osu! now.
However, long vowels such as "おう" "うう" should be romanized into "ou" "uu" instead of "o" "u", since we cannot use a macron in a non-unicode field. It has already taken root in osu! so you probably find it more natural. And using "o" "u" also makes us unable to tell the difference between 2 different words which have the same romaji, for example "Yuka" and "Yuuka". And "ou" "uu" show their actual pronunciation so they help you know how to pronounce them correctly.
For example:
O Touhou
X Toho
O Shippuuden
X Shippuden
Also there are many variants of Hepburn romanization. The two most common styles are Traditional Hepburn and Modified Hepburn. They're basically the same but different in some respects. See Wikipedia for their detailed features. As you can see in osu, we romanize particles "を" "へ" "は" into "o" "e" "wa" so modified Hepburn seems closer to what we have in osu!
tl;dr - Refer to Hepburn romanization when you romanize Japanese. Long vowels such as "おう" "うう" are romanized into "ou" "uu" because we cannot use a macron in a non-unicode field.
See also:
[Rule] Romanisation of Chinese, Japanese and Korean titles
Any suggestion?