Reason for the bosses is because in many games of the same 5 year period also had it so certain attacks would not show up without fighting the bosses.
I've beaten the English version a few years ago and I didn't notice anything like that. The attacks appear as the character levels grow, nothing else. AFAIR, there are eight per character. With half the special attacks for girls consisting of first aid and cheering the party up.
For now, at level 4, they have:
Ranma: a) running away, b) meteor kick (single enemy, moderate damage)
Ryouga: a) some weird-named move where he just taunts enemies with his umbrella, b) bakusai teketsu (little damage, all enemies)
Akane: a) healing (single ally), b) jigokuguruma (Hellish ???) (single enemy gets thrown into the air for moderate damage)
Shampoo: a) healing (single ally), b) shampooing single target (probably should cause a status effect but I didn't notice any)
The thing is, in this game equipment plays a crucial role. I just had Akane (sailor fuku + hammer) one-hit-one-kill most enemies while Ranma barely scratched them. But for managing equipment, you need to at least know hiragana and katakana (kanji are never used in item descriptions as the font is too small) and have an e-dictionary at hand.
Also, there are two plot items, kettle and bucket, which could be always used on the Jusenkyou-cursed characters. Surprisingly, P-chan has the same stats as Ryouga
