Radiant Silvergun

Here's the easiest way to do it, in two tips:

1) To power up your weapons to maximum, work on the achievement. I did this first before tip #2:

2) To gain more lives, play Story Mode more. Each hour grants you a new life. You can "cheat" and leave your console running on pause and it still counts. How many lives you will need depends on your skill. But I was able to beat Arcade mode on my last life and continue using 10 lives/continue, and I was not able to beat Story Mode on 28 lives with my weapons max'ed out to 33! That's for a frame of reference. But take into account I don't suck at these games and there's a few stages, and even more bosses in other stages, that are new in the Story Mode, which I've only played ONCE. You cannot skip stages as you can in Arcade Mode. If you haven't already, work on first, as it's easier and gets you use to most of the game.

Hope this helps.