Man, this is the kind of question that gets me right in the feels. A good Chara and Asriel story that really digs into their relationship, especially after the pacifist route, has to tackle some serious baggage—the shared history, the betrayal, the weirdness of being a ghost and a flower, all that guilt and grief. I keep coming back to one called 'Soil, Ash, and Remembrance' on AO3. It's a post-pacifist slow burn where Asriel, stuck as Flowey but remembering everything, and a resurrected Chara have to navigate rebuilding a world that remembers them as monsters in different ways. The writer doesn't shy away from the painful, awkward silences and the moments of sheer, overwhelming anger. It’s less about redemption and more about two broken beings learning to be something like siblings again, and it hurts so good.
Another one that wrecked me is a shorter piece called 'Golden Flowers in the Ruins.' It’s structured as a series of letters Chara never sends, reflecting on their time with Asriel and the life they could have had. The emotional weight comes from the quiet, intimate observations—Chara noticing the way Asriel’s hands shook when he was nervous, the specific smell of the golden flowers in the castle garden. It’ s not plot-heavy, but it builds this profound sense of melancholy and love that lingers long after you finish reading.