WARNING: The following contains spoilers for the Boruto: Naruto Next Generations manga and anime.
The Naruto series didn't pull any punches when it came to ending fan-favorite romances. Many were left torn seeing Asuma die, leaving a pregnant Kurenai behind, as well as how Kakashi had to kill Rin, someone who loved him dearly. It was also tragic seeing Kaguya separating herself from her family early on, not to mention when Minato and Kushina (Naruto's parents) died. It felt like creator Masashi Kishimoto didn't believe in true love or happy endings.
However, key developments in the manga could resurrect a romance we didn't see come to fruition -- that between Jiraiya the Gallant and Lady Tsunade.
Both were part of the legendary Sannin trio with Orochimaru but they disbanded and went down different paths. Orochimaru became a sinister scientist and terrorist, while Tsunade became a drunk and gambler like her grandfather, the First Hokage of Konoha, Hashirama Senju. Jiraiya, scarred from his mentorship of Nagato and the future Akatsuki members, would eventually wander the world, writing poems.
However, his heart remained with Tsunade, who just never gave him a chance. She knew Jiraiya was a wild beast, but also that duty would always keep them apart. Eventually, when Hiruzen Sarutobi died at Orochimaru's hands, Tsunade -- his former student -- took over as Hokage, and Jiraiya came home. It was to help mentor Naruto the same way he did Minato, knowing Naruto could be turned into a weapon. Sadly, Tsunade sent Jiraiya on a secret mission and his former students in the Akatsuki would end up killing him, dropping his body to the bottom of the ocean. Naruto struggled to forgive Tsunade for the Ero Sennin's death, all while she suffered on the inside as she truly loved him.
But while that story never revived Jiraiya, the Boruto manga has brought him back as a clone. This is in the form of Koji Kashin, the Kara operative who's been plotting against Jigen all this time. He and Amado were waiting for a chance to destroy the alien, and while Jigen has turned into Isshiki, it does seem like Koji's made it out alive. He'd be badly wounded, so once he survives and Naruto, Sasuke and Boruto take down Isshiki, should Koji come to Konoha, this would be the perfect opportunity for him to 'reconnect' with Tsunade.
We're not sure how much of his mind was copied but if he's a blank slate, that wouldn't be such a bad thing. It'd allow Tsunade to make new memories while still remembering who the original Jiraiya was. She might be a tad older, as Koji was grown in a lab, but still, if the chemistry is there the series should follow through. It'd help bring closure to a hero that sacrificed a lot, which is ironic as Koji has followed in the same vein against Jigen.
This could even see Koji discovering himself, becoming a mentor, working with his creator, Amado, as well as Naruto's science team, to see Konoha progress the way Jiraiya could only dream of. This could help Tsunade appreciate the work she's done, too, as her humility often has her downplaying her contributions.
Ultimately, Tsunade never really got to be happy. She lost another lover in Dan when she was younger, so Koji could finally offer her a shot at love. After all, the way she enjoyed seeing Naruto marry Hinata proves that she still believes in happy endings.