People need to use Tenshi's Hisou Sword more.
You mean sword of Rapture? that's what it's called in the latest translation. That move DOESNT EFFING WORK for me. Or in the case of the final boss (pre plus disk), it partially works...Except you can't use it after a Djinn storm! By the time I get the sp back to cast it, the boss's 100% mag wtf pwns me. Wiki says reccommended level was wayyyy higher than I am though, oh well.
Marisa IMO isn't actually that good for bosses. I mean master spark is powerful and all, but when her sp is at 980, and her mag is at +97%, her master spark only nukes for just under 200k more often than not. Meanwhile patchy silent selenes for 70-80k every time she casts it, WITHOUT mag buffs. If you factor in the amount of turns wasted concentrating on Marisa, not to mention the high chance of her losing all her mana from a djinn storm, not all that.
Marisa is a great trash killer IMO though. Asteroid belt is great on anything that isn't resistant to mystic, and Marisa is one of the fastest casters in the game. A bigass master spark comes in handy for bosses sometimes too anyway. I mean nobody can beat marisa at the "oh shit all my guys are dead by my last 2, who are going to die in a turn". Type deal...Or if a boss has a particularly hard "phase", Marisa really helps at speeding thru that trouble area.
Regardless of who is good early game and late game and all that. You get so much exp in this game even when you're benched, that it really doesn't matter if you invested alot in one character at first. It doesn't really backtrack you much to switch.
As for Aya vs chen. I prefered Aya because she was also blazing fast, and I found her speed buffs to be really nice. Her attack spells have their moments, especially since Wind element is fairly rare for the player. But She's not really someone I use to damage a boss much because she's still pretty squishy (just not chen squishy). The delay on her first two moves isn't obscenely low either, they're just like.. 1/2 as long as a normal move..You aren't going to be catwalking like Oren or anything >=P. She's an excellent trash killer though, not to mention that an awful lot of the fast moving highly dangerous enemies like ghosts and cats tend to be weak vs wind and will be 1shot by aya. Those swordfish thingies not so much.