However the game remains playable even without these, and that makes it a marvel of game design. It's pssible to finish the game with the first character alone (Zangetsu) but doing so turns the difficulty all the way to 11.
Your character has a relatively modest jump and reach, which make things quite a bit harder. You don't have other characters to use as bullet sponges so you need to pace your health more carefully. However none of the shortcuts through the levels are available and you're forced to take the longest and more dangerous route every time. On top of this I realized only at the sixth level that the power-ups scattered through the levels are also inaccessible. The result is a brutal quest through 8 levels and some really tough bosses which is as hard as the hardest arcade games of yore. All of this in a game that in casual mode remains very accessible. Truly a small marvel.