For Charming Siege, you close your eyes and pray for good RNG. It can really nastily wall you if it wants to. The best option would be to try staying under Ran as much as possible while holding focus to ensure maximal damage output to end it as fast as possible.
There are a few funny images of nice situations caused by that attack, but I don't have them handy at the moment, I'll see if I can dig some up.
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For the safespot on the finale, you generally lead her to one side and find a spot where none of the bullets strayed by the current phase is able to hit you. Ran follows your movement, so you have to remain on the side of the boss you have led her to, otherwise she will start moving towards the other wall, thus changing the pattern and dissipating the safespot. (This is often done during the 3rd phase) Then, you keep damaging her all the way to the end, altering your position a bit in case the current spot becomes unsafe come a new phase. However, this safespot is not static, and isn't always there. It's luck-based, but I'd suggest trying it out on a real run anyway, since it'll end up helping you a lot (border timing/unfocused damaging/grazing/safety) in case you manage it.