Sorry for the late reply. I don't have a friend with a flashme'd DS, so I can't play the game. And there doesn't seem to be a list of commands in Japanese bulletin boards. But the video on this site was very helpful:
http://club.nintendo.jp/present/p62/index.html
Especially to help with your pronunciation. It looks like a lot of it (boss battles in particular) involves saying what's prompted on the screen, so without being able to read hiragana and katakana it might not be possible to beat it. But here's a transcript of what I heard them say in the video, in the order they appear:
"Sei, no" (seems to just set the rhythm before a group command, like "one, two...") ã›ーã®
"Yuukan na Choukan" (said during the training section, something like "Super-hero form?") ゆã†ã‹んãªã¡ょã†ã‹ん
attacks:
"Panchi" ("Punch") パンãƒÂÂ
"Kikku" ("Kick") ã‚ÂÂック
"Tei" (just a nonsense shout) ã¦ãÂÂÆ’
"Yaa" (another shout) ã‚„ãÂÂÂÂ
(probably other nonsense shouts will work)
"Chenji Bakuretsu" (transformation, "Explosive Change") ãƒÂÂェンジãƒÂÂクレツ
Three-way attacks:
"Rou-ringu" ("Rolling") ãƒÂÂーリング
"Faiyaa" ("Fire") ファイヤー
"Tobira o Hirake" (said to open the door, like "Open Sasame") ã¨ã³らをã²らã‘
during the boss battle:
"Kaze no Byakko" ("White Tiger of Wind") ã‹ãÂÂϋ®ビャッコ
"Mizu no Sei-ryuu" ("Blue Dragon of Water") ã¿ãšã®セイリュウ
"Zekkyou Senshi Sake-burein Sanjou" ("Shouting Warriors Sakebrain Trio(?)") ゼッã‚ÂÂョウセンシ サケブレインã•んã˜ょãÂÂâ€Â
Given the pattern from the boss battle ("Kaze no Byakko" and "Mizu no Seiryuu"), there's probably a few other commands (they match the Chinese Gods of the sky, and each probably is the guardian spirit or whatnot of each of the five warriors):
"Chi no Genbu" ("Black Tortoise of Earth")
"Hi no Suzaku" ("Red Phoenix of Fire")
"Sora no Ou-ryuu" ("Dragon King of Sky")
Actually, those are probably wrong... I'm not real familiar with this part of Japanese mythology and pieced it together mostly from Final Fantasy wikis. Maybe someone else can help.
Also, remember that a Japanse "ou" is pronounced like a long "o" (hold it for two syllables). And the last vowel sound is often unpronounced (especially in English-derived words like Kikku (kick) and Panchi (punch)). If you read along as they say it in the video you should get a feel for it. Hope that helps! If I ever get a chance to play the game I'll be able to tell you more. Do you need three players, or can you do it with just two?
And, if you really get stuck, you could brute force it.
Here's a chart of hiragana and katakana (the best one I could find for this situation). Just write it out one character at a time :-\