On the Disney Wiki, I posted a little about the possible Japanese spellings of each characters name, and I decided to post them here, too. In Japanese, there can be different ways to write your name with Kanji (a similar concept would be 'Elle', 'Ellie' or 'Elli'). What I did was separate them into each possible way that their full names could be written.

Names are written in the order of which they're written in Kanji: last name, first name. There's a space between the last and first name.

Only characters who have at least one Japanese name will be used (i.e. Cass Hamada will be here, but Alistair Krei won't). When and if more characters are announced with Japanese names, I will edit the article.

Hamada family
Hamada can mean 'seashore rice paddy'. Doesn't really describe the family, but rice paddies by the seashores are really pretty scenery, at least.


Hamada, Hiro (ハマダ ヒロ)
notes: Hiro can mean different things depending on which kanji you use. Using 浩 means "prosperous", 寛 means 'generous' or 'tolerant', and 裕 means 'abundant'. May reference his intelligence. Japanese media refers to him as ハマダ・ヒロ (Hamada Hiro).

浜田 裕
浜田 寛
浜田 浩


濵田 裕
濵田 寛
濵田 浩


濱田 裕
濱田 寛
濱田 浩



Hamada, Tadashi (ハマダ タダシ)
notes: Tadashi can mean 'morally correct', righteous, and true. Simply put, his name describes a good, honest person. This might have been intentional, considering his personality. Tadashi is also a common Japanese name. Japanese media refers to him as ハマダ・タダシ (Hamada Tadashi).

浜田 正
浜田 禎
浜田 忠


濵田 正
濵田 禎
濵田 忠


濱田 正
濱田 禎
濱田 忠


Hamada, Cass
notes: Cass is not a Japanese name, so it does not use Kanji. Instead, it uses 'Katakana', which is used by the Japanese to write words originally made using the Latin alphabet (like English). Therefore, Cass is always 'キャス', which would be pronounced 'kyassu', with a quick, almost silent 'u'.

浜田 キャス

濵田 キャス

濱田 キャス


Others


Yokai
notes: Yokai is an actual word, meaning phantom, spirit, or ghost. As such, there is only one spelling for it:

妖怪

This of course likely alludes to his personality. This could suggest many things; he may be hard to find, hidden often, has an ability to dissappear or become invisible, or is incredibly quick (making it seem like he poofed away like a ghost). It can also very simply reference his mask, which is scary like a ghost; and in Japanese folklore, there are a few stories about monsters & ghosts who wear masks.


Wasabi (no Ginger)
notes: Most would know that 'wasabi' is a food, more specifically a super-hot sauce. 'Wasabi no Ginger' can mean Ginger Wasabi ('no' means 'of').

わさび (Wasabi)
わさびの生姜 (Wasabi no Ginger, in Japanese: Wasabi no Shoga)