Well, 1CC'd the game yesterday morning on Slash Mode using Tsubaki/Sumire with a poor score of 470mil(playing for survival.) Basically, I tore through stages 1-5 without getting hit, nabbed 2 extends and ended up with 5 lives by the time I hit stage 6.
Unfortunately, I hadn't practised stage 6 as much as I should have so lost 2 lives, which wasn't a big deal. Fought the last boss with 3 lives, and basically bombed him to death(I had the lives to spare lol.) I wish I'd practised stage 6 more, if I'd completed the level without getting hit, I'd have got to fight the true last boss(a harder version of the last boss.)
Thoughts: Game's difficulty's intermediate. Not too easy and not too hard. Phantom Mode and bomb stock being replenished by 3 upon death mainly contribute to Akai Katana Shin being more forgiving than other shmups.
I feel the bosses are quite hard in this game, had the most difficulty dealing with the stage 3, stage 4, stage 6 and 7 bosses. Stage 5 boss seems difficult at first, but she's actually not that hard at all, and her patterns are rather forgiving, all the way up to her last pattern.
I had a lot of fun playing this game, now that the grinding's over, I'm gonna have some fun and play for score.