Nabu

Nabu is one of the love interests of the Winx girls. He is part of a wealthy family that was arranged to be married to Layla. However, she wasn't interested and her parents' urge to make their daughter get married made her indifferent towards having a romantic interest and didn't mind being single. However, Nabu was very interested in her not as a betrothal but as someone who wanted to be an actual love interest to her. He struggled several times to get her interested.

He remained her love interest after that. He was her boyfriend for the rest of Season 3, his first appearance, but then, Nabu was nearly killed in Season 4 and was put into a coma. Layla was grief-stricken and wanted revenge against the wizards who did this to him.

Ultimate Story
Nabu made his first appearance with the other specialists at the very end of the Ultimate Story special: The Celestial Winx. Unless his original incarnation, he wasn't taken out. A long time ago, he lived during the era that the Original Celestial Winx did. He was to be married to Aisha but was interested in Layla, so against the wishes of his family and the royal family of Tides, he dismissed his arranged marriage with Aisha and asked Layla to be his girlfriend.

When Layla and her friends friends graduated from Alfea, he was there to witness it happily. The Great Wizard then appeared before them and reward them by making them his trusted followers. He also made them the Celestial Winx. The girls were then sent off on their first mission to find and defeat Malicet. Nabu and the other guys saw the girls on their way, awaiting their return from their mission.

However, things did not go well and girls couldn't defeat Malicet, forcing them to sacrifice themselves. When the Great Wizard delivered the news about the girls' sacrifice, Nabu and other guys were grief-stricken. They decided to take on a journey to meet with the Enchantress of Magix so that they could find a way to reunite with their girlfriends.

When they able to meet with the Enchantress, they begged for her to find a way reunite with their girlfriends. She did mention, however, that there was no way they can reunite at the moment. There was one way that they can: she needed to put their entire realm in a cryo-status until the Celestial Winx were to return. Desperate to see their girlfriends again, they conceded and had her put all of their worlds into a status that lasted for 4000 years.