What should I buy?

[Gaijin]

Yes, I've researched the available documentation, but unfortunately, much of it is dated.

My character:
Shinigami
Level:17
Specialization: Spirit - Aggressive

I just ranked up to Squad Member.  According to Inazuma's edited Medusa's Guide for Shinigami, which seems like a good document, I should now buy "Way of Destruction 18: Green Flames (Spirit)| 6,000 spirit skill". That's the dated part; the specified ability doesn't exist.

What exists?  Way of Destruction 14: Green Flames (Spirit)| 2,500 spirit skill

My questions:
Which ability should I buy? I can afford any of them.
WoB doesn't have a bank.  Where do we put our money for safekeeping?

[Setoku]

Well, seeing as I don't know anything about the re-balances Shinigami went through after I switched races a long time ago, I'm gonna go ahead and say buy 14. It's the same spell, just most likely nerfed in choice of fairness. As for your money, you keep it. You ain't gotta put it nowhere. Just spend it like a maniac... (Me) or save up for shards or something.