Continued brainstorming of plot

I remember the deal Enfer was going to offer Dante. There was something about dante's soul running out of energy, so she offers to remake her soul and give her another fallen seraph's body. This is so that Dante won't be bothered to steal enfer's body. Anyway, a human soul is always too weak to inhabit a seraph's body, and a seraph's soul is too fiery for a human body. So there. Fallen seraphs symbolize a loss of faith, hence the profusion of fallen seraphs in the world beyond the Gate aka more beautiful people. I have come up with reasons for envy being the one to guard her. First, since he is dante's son he is the most trusted. Secondly, he is the only one who can overpower her. All the homunculi match her in speed and ability, but enfer's strength gives her an edge over them in that she can fling them away. However, envy, being much more massive than he looks, has too much inertia for her to be able to use her strength to throw him away. The moment he sits on her she can't move.. -.-
So initially they think enfer is a boy, but then envy walks in on her showering/changing. He doesn't see much, but enough to know she's female. Then of course Dante knows. However, how will she react? Will she make enfer dress in gowns and stuff or just continue with her clothes? Ah, perhaps enfer came to Dante on a stormy night and made the deal with her. Then she accepts dante's hospitality and so goes to bathe. Envy, bringing a change of clothes for her, discovers her true sex and hence tells Dante, who provides a change of female clothing instead. So what does enfer want from Dante? Maybe to learn the truth behind alchemy? Admittedly Dante doesn't know everything, but she's the most knowledgeable. Enfer wants to go back to her own world and hence needs to know more about alchemy. So in return for dante's hospitality enfer works with envy on missions if required. Envy is of course told to protect her with his life. This begets the question: how did enfer know about Dante in the first place? How did she think to make a deal with her? Is she going to meet a homunculus? How should I start the story? From the point where she talks with Dante, or before that, when she is a state alchemist? Or way before that, with a prologue telling of the legend of the girl from the sky, told to children at bedtime? Then I'd have to write a story within a story. So it'll be a legend? Maybe when she first appeared in this FMA world she hadn't a human guise yet. And thus was born the legend, which probably happened in xerxes? Then about a 100 years later, or depending on the time period(looks like I'd need a lot of reading up. Thank god for mercies like wiki!) she exists as the Irritum alchemist, so named because she makes things 'disappear', actually turning matter into energy which she stores. This allows her to achieve superhuman feats, the way a philosopher's stone does for its user. Except she needs something to store the energy. What could it be? Maybe a jewel she calls irridium? Hmm.. What Colour? Black, but with irridescent colours? Yes, and harder than diamond. It looks as if a star has been trapped within the stone. Embedded in her flesh, just under the collarbone. Or on her forehead; she could cover it with.. Her hat? Or maybe just silk. Or perhaps a forehead ornament when dressed as a female. So yes, her fighting style is never flashy, unless she's really threatened. Perhaps her fighting style could also incorporate shadow clones (kind of like naruto, heh heh.) to confuse the enemy while the real deal sneaks up and changes him to energy to be stored/apprehends him as needed. These shadow clones require her stored energy, because they form real matter, but these then return to her stored energy after the battle. But she probably doesn't tell people the truth behind where she stores the energy. Perhaps she'll have a decoy jewel- an amethyst on her silver bangle.. What should she fight with in hand2hand combat, though? Perhaps foot-long scythe-like blades? Because I like that style of fighting; it's dazzling and sneaky, in slashes and speed-dashes and twirls and leaps, graceful and lethal like a praying mantis. The principle of her attacks is to strike viciously, then retreat from counters, then start again. The end of the combo is the nicest with the 2 blades slashing down like the deadly strike of a mantis, before she does a backflip to get away from the enemy's possible return strike. Damn.. How will I convey that in my words? Anyway, she probably doesn't carry weapons around, so she'll transmute them as and when she needs them. She doesn't even need to clap to transmute, but to hide this fact, she wears gloves like mustang's, except maybe black with a gold transmutation circle. So in fact, she doesn't really use this world's alchemy, and although she knows the theory and is capable of applying it to solve cases in her mission as well as assess her enemies, she actually doesn't genuinely understand alchemy hence needing dante's help.
But then, what kind of adversary will the story have? How do I make it eventful? How do I integrate romance into the plot if I have no real understanding of it? I don't really want any sexual content in the story, more of a budding relationship between her and envy which is sometimes dark and cruel yet intoxicating; never too gentle and fluffy. but sex-stuff is the only kind of understanding I have of romance (read too many of such stories, especially in yaoi..) .. Pathetic, huh? Please don't tell me I need to be in love to be able to write such a story, because then I'd never be able to write this story.. -.- geez..