It does go away if you don't keep the inactive player's counter up.
In Arrange mode, there are 2 counters/meters on the bottom of the screen. One for Reco, and one for Palm. Your bullet reflection ability is always based on the inactive player's counter. Once it hits 0, that character can no longer reflect until you raise their counter again. To do that, you switch characters, and any point item you get as that character recharges your counter, while you use the counter you were increasing while you were using the character you were using before you switched.
For example,
Say Reco is the active character with 1000 counter, and Palm is the inactive (read: Reflecting) character with 5000 counter. Reflect bullets using Palm, and each reflected bullet will cause a stream of falling point items. Because of this, it's best to let bullets accumulate in your force fields before you send them flying. Doing this properly will give Reco's meter a nice boost. Keep in mind that (well, it seems) that the more bullets you send off, the more the reflecting character's counter decreases. Once Palm's counter is completely gone, he can't reflect anymore. But since you've been charging Reco's counter, you switch to her and repeat the process.
That's the basics of it, really-- but playing like this won't net you a very good score.
In Mushihimesama Futari, there are 2 colors of point items. In arrange mode in particular, the green ones will charge your counters as well as your multiplier counter at the top of the screen. You get that by using your unfocused shot, and by reflecting bullets. There are also 2 sizes of point items as well, small and large. You get small ones by reflecting bullets, and you get both small and large ones depending on what you're destroying with your unfocused shot.
However, the blue items are the ones where the score comes from. You get these by shooting enemies (and bosses) with your focused shot. The catch is, your reflective barrier is always active when you're using your focused shot, and it depletes fast when you use it. So what you want to do is balance how you use your shots so you can not only increase counters, but survive as well-- and score when you can.
If you manage to get both characters' counters to 9999 at once (really easy in Ultra Mode), you can trigger 'Fever Mode', where both characters' counters decrease to 0, but every point item you get is large instead of small. When you're in this mode, it's best to just hold down your focused shot and cash in for points while reflecting bullets at the same time to get a major multiplier counter boost.
It's all really confusing, but once you play it, it makes a lot more sense. Overall, it's a risk-reward sort of thing. In Arrange mode, you can take it easy and make sure your characters can always reflect, or you can take a risk and cash in for score.
Oh-- and Arrange modes have Autobomb enabled-- which makes it a lot easier.
Arrange Ultra is still a nightmare if you don't know what you're doing, though :V
