Curse you, witches. My brain is working overtime. Hourglass demands a meta prompt, which this is. Quick and dirty meta, mirroring like the halves of an hourglass, one filling as one empties.
Probably better meta-ers than I have noted this, but my little verse for this challenge has made me consider the canon paths of Spike and Willow, and the way they reverse one another out.
In season 4, we see Willow increasingly integrated. Yes, she's slightly alienated from the other Scoobies, but that's really a process they're all going through. She's finding witchcraft, finding college to her taste, finding Tara and some inner life she hadn't apparently known or acknowledged previously. Meanwhile Spike, very evidently, is alienated from everything: he loses Dru, Harmony isn't a substitute; the Gem of Amara was a great quest which he loses; and then the chip completely wrecks his sense of self, and his participation in the demon community.
Season 5, perhaps less strongly, their paths waver in opposite directions. Spike gets closer, acts with good intent, increasingly putting the team (or his definition of the team - Buffy, Dawn, maybe Joyce) ahead of his demon preferences. He is prepared to sacrifice himself for Dawn, at the end. Willow faces tougher times, especially in the hint of the darkness to come, and in the final showdown with Glory is at least 50% focused on Tara, who she might save only to see the dimensions fall anyway. At that classic moment of Spuffy connection ("I know you think that I'm a monster, but you treat me like a man." "Come in, Spike." Across the hallway barrier), Willow and Tara are aeons apart, with Tara's mental barriers holding Willow away.
Season 6: Willow has a purpose as the season opens; Spike is holding on by a thread, aimlessly babysitting away. Spike gets what he wants as Willow loses it (Tabula Rasa); Willow struggles back to friends and balance as Spike increasingly loses his. Spike definitively loses Buffy by his own act; Willow definitively loses Tara by someone else's (Seeing Red). Spike goes looking to improve himself (deliberately not saying redeem, but whatever he sees the soul as it's a 'stop doing that bad stuff' brake); Willow deliberately turns to the darkest of the dark. But Willow's saved by her friend, being very human. Spike's saved (query, debate), by a lurking demon. Opposites, see?
Season 7 to round off. Willow's now saving herself, with purposeful, difficult steps towards redemption, and an uncertain grasp of her former skills. Spike's lost the plot, wandering and crazed; then helpless and damselly waiting for rescue. Season 7 finally sees their paths converge and parallel as they take up similar roles against the first, but even there, the mirroring is acute. Willow researches an item of great history and connection to the Council. Spike casually slings on an item provided by known Big Evil, mechanisms uncertain. Willow radiates bright light, and Spike is consumed by it. But all, finally, in the same good cause.
Too tenuous? Maybe. But I'm avoiding Deer Antler Remix nemesis and it's past my bedtime, so gimme a semi-free pass please.