Darkness in the Heart is a pretty cool concept. I actually had an idea a while back of making something like this myself. :V
Just a couple suggestions. First, maybe consider increasing the wait time between roulette rolls--or at the very least make Seija's screen-flip delete all bullets onscreen, because when it activates while the screen's full of bullets, it's pretty much insta-death.
Second, don't leave the roulette 100% up to chance--maybe make a system where the screen-flip and Komachi distance thing are a bit rarer, since they're "status" effects so-to-speak, so you don't want those getting spammed lest you wish to annoy the player while leaving the screen rather devoid of bullets. At one point, I rolled Komachi's distance thing 4 times in a row, and it got rather boring for a bit. At the very least, make it so the random number generator can't select the same pattern twice in a row.