Sea-salt ice cream

Sea-salt ice cream (シーソルトアイス) is a type of ice cream found in Twilight Town and Radiant Garden. It appears throughout the  universe, but made its first appearance in Kingdom Hearts II. Kingdom Hearts II is also the only game in which the ice cream features as an attainable key item. The ice cream's flavor mixes both a salty taste and a sweet taste.

An interview with Tetsuya Nomura after Kingdom Hearts II explained that Nomura first tasted sea-salt ice cream at a trip to, a smaller resort of Disney's parks in Japan. He liked the ice cream very much and decided to work with Disney to have it put into Kingdom Hearts II. He also said that the idea to put the dessert into the game came to him when he was thinking about what the kids in Twilight Town do and eat over summer vacation.

Kingdom Hearts Birth by Sleep
Following Terra-Xehanort's defeat and their subsequent ejections from Hollow Bastion, Lea buys two sea-salt ice creams from Scrooge McDuck and gives the other ice cream to Isa.

Blank Points
After Terra-Xehanort is taken in as an apprentice, Ansem the Wise and Ienzo eat sea-salt ice cream together while walking down a hall of the castle in Radiant Garden. Axel, Roxas, and Xion are also seen eating sea-salt ice cream together in Twilight Town as they had during their days in the Organization XIII. Roxas and Xion then say Sora's name in unison.

Kingdom Hearts Re:Chain of Memories
Shortly after his birth, Roxas passes Hayner, Pence, and Olette in Twilight Town. The trio each has their own bar of sea-salt ice cream. He later eats his own along with Axel on top the clock tower.

Kingdom Hearts 358/2 Days
Axel treated Roxas to sea-salt ice cream on the Twilight Town Clock Tower, saying it was "icing on the cake", after Roxas completed his first mission and reminding him they sat there the first day Roxas got his new name. He then suggested that he and Roxas should meet each other to eat ice cream every day after they completed their missions, stating going back and forth to the Castle That Never Was was boring. After Axel left for his mission in Castle Oblivion, Roxas invited Xion to join him. Soon Roxas, Axel, and Xion began eating ice cream together after their missions. Sea-salt ice cream is Axel's favorite flavor.

On Day 118, Roxas is sent on vacation and has no idea on what to do. After rejecting Xion's offer of practicing with the Keyblade, he once again looked at the notice posted in the Grey Room. While looking at the notice that said "Operations Closed for Vacation", Roxas thought, "What to do? What to do?". Then he concluded the scenario saying the word "Ice cream". This perhaps shows that Roxas had learned to like ice cream ever since Axel had given him one.

Axel first notifies Roxas that some ice cream sticks have the word "WINNER" (あたり) on it, and can be redeemed for a free ice cream bar. on one of their later meetings, after Roxas found a WINNER stick, but kept it secret. He later bestows the stick to Axel as a farewell gift when he leaves Organization XIII.

It also acts as a symbol of the friendship between the three of them, most notable when Roxas asks Xion who he will eat ice cream with as she vanishes.

Kingdom Hearts II
Hayner, Pence, and Olette also enjoy this ice cream, usually eating it together. In one of Roxas's memories, Axel offers him a stick of sea-salt ice cream before their parting. After Riku steals the digital Olette's Munny Pouch from Roxas, he asks DiZ what to do with it, and DiZ jokes that they could use it to buy ice cream.

When Sora arrives in Hollow Bastion, he sees Scrooge McDuck, who is trying to recreate the recipe for sea-salt ice cream. Through subsequent visits, Scrooge comes closer to reinventing the flavor and ultimately succeeds.

Riku left a sea-salt ice cream with a picture of Roxas and the gang from the Simulated Twilight Town as clues for Sora, Donald, and Goofy. Donald took an immediate liking to the ice-cream, and ate it.

Ansem the Wise was very fond of this ice cream, and often ate it while conversing with King Mickey, and later used it as the password for his computer in the Old Mansion, which Sora, Donald, Goofy, and Mickey use to enter the Simulated Twilight Town.

Kingdom Hearts 3D: Dream Drop Distance
Axel and Roxas eat sea-salt ice cream in Lea's dream just before his awakening.

In the Kingdom Hearts II manga, Roxas falls off the Clock Tower while trying to catch his ice cream that was sliding off of the stick. If you look closely, the ice cream stick had "WINNER" imprinted on it.

In the main menu for Kingdom Hearts II, Sora is seen to have had sea-salt ice cream as well, since the stick is hanging from his mouth.

In Kingdom Hearts 358/2 Days, sea-salt ice cream is a recurring element in the game's plot and the system icon that is seen upon the initial startup of a Nintendo DS.

Kingdom Hearts III
During their training in the Secret Forest, Lea and Kairi share some sea-salt ice cream to celebrate them becoming Keyblade wielders, but Lea drops his after seeing a vision of Xion and sheds a tear. Before the final battle, Lea sits on the Twilight Town Clock Tower eating sea-salt ice cream when Saïx comes in and discusses his past life with Lea and talk about a girl they made friends with. After Xehanort's defeat, Lea, Roxas, and Xion sit on the clock tower when Isa shares ice cream with the trio along with Hayner, Pence, and Olette. After eating the ice cream, the gummi ship picks up the group and takes them to the Destiny Islands to celebrate their victory.

Trivia

 * In the DuckTales (2017) first-season finale "The Shadow War!", Mrs. Beakley makes Huey, Dewey, and Louie a dessert using sea-salt ice cream, saying it was Scrooge's favorite and a "common farewall ice cream in certain parts". The latter is possibly a reference to how the ice cream appears during especially poignant final segments in the games— specifically, Roxas' final week of summer vacation in Kingdom Hearts II, and the last ice cream he shares with Xion during the end of Kingdom Hearts 358/2 Days. Roxas also leaves a WINNER popsicle stick for Axel to find after he leaves Organization XIII, and shares another ice cream with him the last time their hearts meet on the clock tower in Twilight Town during Kingdom Hearts II Final Mix, after Roxas' mental battle with Sora.