“I don’t want to be president. I just want to be a nice person,” Katy Perry announced midway through her concert Monday, Sept. 10, at the Theatre at Ace Hotel.

“I just want to make people happy,” the L.A. singer added at the close of an energetic and unabashedly joyous 16-song set, and she clearly succeeded with an adoring crowd that filled the cavernous old theater’s balcony.

But Perry also got heavy at times, musing at length about God, nature, loneliness, alienation, the music industry and her search for a spiritual purpose over the past year. The show might have been a warm-up gig for her appearance at the KAABOO festival in Del Mar on Sunday, Sept. 16 — as well as a way for her to thank her assembled family members, record company staffers and Citibank corporate sponsors — but Perry’s disarming performance and confessional insights were unexpectedly vulnerable and ultimately moving.

Two weeks ago, Perry and her coed seven-piece band — two keyboardists, two backup singers, a bassist, a guitarist and a drummer, all wearing black suits with white ties tonight — wrapped up the final international concerts of the nearly yearlong Witness tour, which included three sensory-overload nights at Staples Center last November. At the relatively intimate Theatre at Ace Hotel on Monday, they performed without the tour’s massive sets, pyrotechnical special effects, multiple costume changes and crew of sexy dancers.

For the show-opening “Hey Hey Hey,” Perry prowled the stage in shiny red sneakers and a form-fitting leopard-print cat suit whose shoulders billowed out like a satin life preserver. Her short, bright “slime green” hair flashed luminously in the glow of an occasional blacklight. The colorful, neon-limned stage set resembled a surreal bedroom, with doors framing the musicians on two sides of the stage, and the drums mounted on a tall riser that looked like an oversize dresser. A couple of tall mod lamps loomed like trees on twisting, curving poles as brightly animated video images were projected on the back wall of the stage.

“Who cares what everybody else thinks?” Perry shouted midsong.

There was a lot of glitter and glamour in the room — and that was just the crowd. One man wore a shiny gray suit whose lapels were lit up by a border of flickering green neon lights. Women were decked out in emerald-green sequin dresses and rainbow-colored sequin blouses, and some men shimmered in sequin shirts. A trans woman floated by in a dreamy, soft-pink floor-length gown, and a young man sported a bright blue wig in honor of one of Perry’s past looks.

The second song, “Chained to the Rhythm,” was harder and more compulsively driving than the studio version on Witness, with the low end of the bass literally shaking the theater’s walls. The entire audience was standing, with many fans squealing in delight.

“Some of us were organizing our sock drawers,” Perry told the crowd to introduce an anthemic version of “Teenage Daydream,” explaining how she and her band were just starting to get back to their home lives after the long tour for Witness. “I went to Burning Man, so my brain is mush. So let’s do a cute show at the Ace,” she said, feigning surprise about the concert, which was announced on short notice.

Credit: Neilson Barnard/Getty Images for Citi

Credit: Neilson Barnard/Getty Images for Citi

“This is intimate. I love being a massive pop star,” Perry added guilelessly, “but I love being close to people.” She was so close to fans in the front that she offered to show them her tonsils and held out her arms so they could smell her perfume.

The singer donned a pink Flying V for a winsome and driving “Hot N Cold,” and then tried to recruit help from the audience to rap the Snoop Dogg verses on “California Gurls.” She invited the guy in the blue wig onstage but he initially demurred, so she plucked the wig off his head and triumphantly held it aloft like Salome brandishing the head of John the Baptist. Another man climbed onstage and rapped the part instead, drawing cheers from the crowd before a smiling Perry advised him, “Get off the stage!”

Introducing “I Kissed a Girl,” she reminisced about “these hits they used to play on a thing called the radio. It was a different time. It was 2008. Now we’re just fluid.” Perry and the band segued from their cool, newer arrangement back to the song’s earlier version, complete with a rad heavy-metal solo.

“I’m capable of anything,” she sang, ad-libbing a quick, proud aside — “Obviously!” — on “Dark Horse.” This time, a shy girl came out of the audience and rapped the Juicy J break for an approving Perry. “All killa, no filla,” the singer bragged after the heavy-swinging rap of “E.T.,” which was elevated by its triumphant pop chorus.

“I was born in 1984. I’m 33 … and I really enjoyed partly some of the ’90s,” Perry said, listing Alanis Morrissette, Garbage, Fiona Apple “and, of course, No Doubt” as among her favorites from the decade. “I’m going to do a cover, if that’s OK.” But before launching into a stirring remake of Joan Osborne’s “One of Us,” Perry talked about her spiritual evolution and advocated that people “connect with God, connect with nature” and get to know their neighbors instead of spending time on social media.

“Some of us feel really alone. I see the sadness in people’s eyes,” she continued, and all you had to do was walk a few steps outside the magnificent theater and see the gaunt, hollowed-out faces of homeless people begging for change to recognize the cold, separate worlds many of us live in. “I don’t have any fear anymore … because I know who I am. I believe in God — she is incredible!”

With her hands dutifully behind her back, Perry delivered Osborne’s delicate ballad in a rich, moody, low voice. “What if God was one of us? Just a slob like one of us. Just a stranger on the bus,” she sang, tossing in a new aside, “except for Pope Francis.”

“I was a hoarder in a very small room. I would eat [my friend’s] snacks. I was a very bad roommate. I was a struggling artist, playing the Hotel Café,” Perry admitted before strumming a stark and poignantly affecting rendition of the early heartbreak ballad “Thinking of You,” her voice arcing and aching over the band’s subdued murmurs of countrified soul.

The romantic intensity deepened so much with a wistfully longing version of “The One That Got Away” that Perry had to urge the crowd, “Don’t get too sleepy,” to set up the upbeat dance pop of “Part of Me,” which got fans back on their feet again. The blue-wigged fanboy clambered out of the crowd to dance with Perry, and he credibly rapped the Nicki Minaj part on “Swish Swish.”

“I can’t pull someone out of the audience every time I need something covered,” Perry joked.

Light pink balloons rained down from the balcony for the evening’s penultimate tune, “Roar,” which was another song that sounded punchier and more danceable than the original studio recording, from 2013’s Prism. The set-closing “Firework” stirred up more sadness for all those lost and lonely people (“Do you ever feel like a plastic bag drifting through the wind wanting to start again?”) before the chorus kicked in with an uplifting force. The lyric evoked imagery from Fiona Apple’s “Paper Bag” and Neko Case’s 2002 song “Deep Red Bells” (“Does your soul cast about like an old paper bag past empty lots and early graves?”), but it was nonetheless a touching moment.

Backed by just a drummer and guitarist, Katy Perry protégé Cyn opened with a short set. She had a clear, soaring voice, but Cyn’s sometimes plain lyrics didn’t always match her better melodies. There might be a good song hidden somewhere inside “Alright,” but the version Monday night sounded overproduced and muddy instead of exuding the live vibrancy of Perry’s own music.

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