Despite the darkly romantic ambiance, it was impossible to miss Joaquin Phoenix at Zebulon, the shuttered Brooklyn music venue that has been reincarnated as a Los Angeles hotspot in Frogtown (complete with its original slab of a bar). Not because it was Monday evening and the Hollywood premiere of “Joker” was just two nights earlier or because his longtime publicist, Susan Patricola, and his elegant girlfriend Rooney Mara, were perched nearby. It’s because the hoodie-clad actor was shouting his big sister’s name in that unmistakably husky voice: “Rain!”

And all eyes were on Rain, the eldest Phoenix sibling, as she took the stage. “We’re playing you songs from my upcoming record, ‘River,’” she said, referencing her late brother, bandmate in Aleka’s Attic and, more recently, muse. Both Joaquin and Rain were present the night he died on Halloween in 1993; 25 years later, she found herself inspired to address the tragedy through music. The resulting song collection — her debut as a solo artist — serves as a soulful meditation on the theme of grief and loss, whether it’s the finality of death or the end of a relationship.

But there were also moments of levity, like when Rain set down her guitar midway through the ballad “Time Is a Killer” and started tap-dancing. “Some of these songs are pretty somber but I find myself smiling through them because of the energy in the room,” she said. The Phoenix clan can take credit for that — they all came out to support Rain, including younger sisters Summer and Liberty and the family’s matriarch, Arlyn.

Rocking aviators and a low-cut black ensemble, Rain’s look evoked iconic troubadours such as Patti Smith. But the vibe was intimate and cozy — not exactly rock ’n’ roll. Rather than stand for the show, many people in the crowd proved that they weren’t too cool to sit on the floor and kick back, which made the venue look not unlike an enormous living room. But Rain wasn’t afraid to make people uncomfortable. “We can talk about the elephant in the room if you want,” she said in between songs.

“The Dodgers!” someone shouted.

“I was thinking about death,” she said.

“Let’s talk about death, shall we?” Rain continued. “I mean, just more, in general. And let’s comfort the people who have people who die. Like us — all of us — right? And by ‘comfort,’ I mean: Let’s not change the subject. And let’s try to be there for each other more. Because it’s the one thing that we all share even if we don’t agree politically.”

“Who knows what death is?” she asked the audience. “It could be the most magical thing. We’re so terrified of it — we’re so scared …. I appreciate you allowing me the opportunity to say it out loud in front of you tonight.” Then Phoenix crooned her first single, “Immolate,” which was released on River’s birthday (Aug. 23). “It’s for everyone who has lost loved ones,” she said.

And while Phoenix capped her set with a tune titled “Hey, Heartache” — “it’s a real upbeat jam,” she joked — it ended on a sweet note. “There’s one really happy thing,” Rain said. “If she doesn’t bail, my sister Libby — Liberty Butterfly Phoenix — is going to sing with me on this.”

As an encore of sorts, Rain performed “Lost in Motion,” a song with a very long history. She said: “I wrote it with River and [producer] Kirk Hellie. Please enjoy this song.” The show wrapped with a display of love and affection offstage — long, warm embraces between the four remaining Phoenix siblings — which felt like a family affair, or even a memorial. Because memorials, as they say, are actually to benefit the living, not the dead.