I think I cleared it before in DOA4 and I was able to clear Kokoro's in 5. I've seen people say her's was hard. Is doing Hayabusa's command training going to be real frustrating? Sometimes I have to rely on button mashing and hope to get lucky in some of the moves. I did Christie's too which I saw people struggled with, as did I. I'm just put off in trying it if I won't be able to complete it in reasonable time and get irritated. And it sucks since you can't save progress.
It's Hayabusa's Izuna drop or combos that include the Izuna drop that people usually have trouble with. It's easier if you have an arcade stick. Unfortunately I only have a dpad so it took me a while. I personally think Akira's command training is the hardest especially his one frame knee move. --- "Relax and let me do all the work," says Morrigan Aensland to Ghost Rider.
Raijin isn't so bad...the biggest problem is the combo message that appears on the screen. It kind of ruins the input for you if you try to input the commands while the message is up there. (like all the other moves)
the input window is way sooner than the messages appear..it's a bit easier once you realize the right time to input the commands.
Check out this thread, I made a post for someone who said he gave up on Raijin.