When a popular duo or group breaks up, the public often hopes for a reunion. Sometimes it happens, sometimes time runs out.

A Sunday Manoa reunion could have sold out the Waikiki Shell if Peter Moon and the Brothers Cazimero had been willing to set aside differences — but when Moon was institutionalized after a career-ending stroke in 2005, a dream ended forever. On the other hand, when Don Ho and the original Aliis decided to let bygones be bygones, they sold out shows in Hawaii and on the mainland.

Place Hapa in the dream-come-through category this weekend, when founding members Barry Flanagan and Keli‘i Kaneali‘i play a two-night, four-show engagement at the Blue Note Hawaii.

It will be the first time in 17 years that Kaneali‘i and Flanagan have performed together on Oahu, and the 6:30 p.m. show on Sunday sold out more than a week in advance.

(Some seating is still available for a second show on Sunday and two Monday shows.)

“I think it’s spiritual, it’s really spiritual right now,” Kaneali‘i said last Friday, calling from his home on Kauai. “I’ve been attending church with my wife — I just got married two years ago. It’s changed my life and gave me a foundation for myself, and so when Barry called, I said, ‘Let’s try it out.’”

Kaneali‘i dreamed recently about playing music again with Flanagan, he said — and when Flanagan called, Flanagan said he’d had the same dream.

Born and raised in Papakolea, a Roosevelt High grad, Kaneali‘i was living on Maui when he met Hawaiian music enthusiast Flanagan in 1983. Flanagan — New York City born, New Jersey-raised — had been living in Colorado when he discovered the music of Gabby Pahinui and heard Hawaii calling him. He came to Hawaii for the first time in 1980 and made Maui his home. (Flanagan, who was performing last week and unavailable for an interview, continues to live on Maui, where he performs and gives guitar lessons.)

“I met Barry at a party at my friend’s house,” Kaneali‘i said. “We played for the first time together there. He played lead, I played rhythm.

“I knew Hawaiian, he was learning Hawaiian music. He was playing Hawaiian music, I was Hawaiian but I was playing contemporary music, so we kind of meshed. When we met it was magic, you could say.”

THE DUO — they chose the name Hapa because Kaneali‘i was Hawaiian and Flanagan was not — worked together on Maui for almost a decade before making their first recording. When they did — their self-titled debut album was released by Coconut Grove records in 1993 — they launched it with one of the best-executed promotional campaigns Hawaii would see in the 1990s. Kaneali‘i, Flanagan and their management team started on Maui where they were already known and had a strong following. Next they went to “neighbor islands” where local music radio stations were more open to new artists and their music than the radio stations on Oahu.

When Hapa finally came to Oahu, it was on a groundswell of excitement that Honolulu radio stations could not ignore. The album became one of the biggest local releases of the year.

The wave continued into 1994 when Hapa won in five categories at the 1994 Na Hoku Hanohano Awards: Album of the Year; Group of the Year; Contemporary Album of the Year; Single of the Year for “Ku‘ulei Ku‘uipo”; and Best New Artists.

Flanagan earned an additional Hoku for his work as the producer of the album, and another one as co-composer of the Hoku Award-winning song of the year, “Lei Pikake.” He also set an unofficial Hoku Awards show record with the length of his acceptance speeches — an average of more than five minutes for the each of the six awards.

Hapa released two albums almost simultaneously in 1997, but Hawaii wasn’t ready for where the duo was going. The official second album, “In The Name Of Love.” was an imaginative and powerful leap beyond the hapa haole frontiers of the first. The second, “Surf Madness,” was an homage to the surf rock sound of the early 1960s; attributed to “Axel and Berneldo,” it revealed a surprising facet of their repertoire.

Neither album came close to the commercial success of their debut. Neither won any Hoku Awards.

The duo returned to their familiar sound in 1999 with “Namahana.” The songs were soft ballads and soft instrumentals built around Kaneali’i’s voice and Flanagan’s virtuosity as a guitarist.

In 2003 Kaneali‘i ended the partnership for reasons he chooses to describe as “differences.” He continued to play music in Hawaii and in Japan; in 2009, Kaneali‘i released a solo album, “Kauai,” that included five newly written songs,.

After the original duo parted ways, Flanagan recruited Nathan Aweau, a 16-year member of Don Ho’s backing band at the Waikiki Beachcomber who was already a Hoku Award-winning recording artist, to join Hapa. That partnership earned Hapa an Album of the Year for “Maui” in 2006; this time with both members of the duo handling the producers’ duties. “Maui” also won Contemporary Album of the Year, and Flanagan earned an individual Hoku for his work as one of the album’s graphic designers.

When Aweau resigned from Hapa in 2010, Flanagan recruited a long-time friend, Maui-based singer/songwriter Ron Kuala‘au. More recently, Kapono Na‘ili‘ili has been Flanagan’s partner.

The reunion of Flanagan, 63, and Kaneali‘i, 61, brings the story of Hapa full circle — at least for these two nights at the Blue Note. In advance of the Oahu appearance, the duo has performed in at concerts in Seattle and Virginia.

“It’s so nice to have this second round, this second time again, and I’m just thankful,” Kaneali‘i said. “I’m thankful to God for this second time around.”