Such plot as there is deals with the struggle between Steamboy Ray Steam's grandfather and father over their mutual invention, the Steam Ball, a kind of hyper-efficient steam storage battery, with Ray in the middle. Grandfather Lloyd believes in pure science for the advancement of humanity. Father Edward, embittered by his disfigurement in a lab accident, has sold out to the "O'Hara Foundation," who are in reality ruthless weapons manufacturers and dealers. The struggle over the ball is somewhat complicated by the intervention of the British government and rival inventor Stephenson, who is perhaps not as good a guy as he initally appears.
Character development is minimal, with the possible exceptions of Stephenson and his assistant, who acquire some ambiguity as the plot unfolds. The mad scientists stay mad, and Ray is spunky and heroic throughout. Steadfastness is actually a virtue in one character, Miss Scarlett, the bratty and spoiled scion of the O'Hara munitions empire, who sees nothing wrong in the family business. I kept expecting her to see "the error of her ways", and it DIDN'T happen. The closest she comes to a moment of doubt occurs whan she sees a "steam trooper" killed in front of her, and has a moment of squeamishness when she realizes that there is "a man inside the machine." Kind of refreshing, actually.
As I said, very fluid and believable animation, particularly involving the steam machines, and wonderfully intricate design, especially in the Steam Castle. A pity there isn't more story to go with the wonderful effects. I was looking forward to something like an industrial-era "Princess Mononoke", but only got "Akira" warmed over. Miazake need not fear for his laurels as a storyteller. "Howl's Moving Castle" based on the novel by Diana Wynne Jones will be out soon--.