When Malik uses his "Eternal Serenade" Mystic Arte to finish off Spoiler:Lambda, the final boss of the main storyline, he will claim it to be the last time he uses said move.

However should the player later win any battle using this move in the "Lineage and Legacies" mode set after the main story, with the above criteria achieved, a special victory scene will play where Sophie points out that Malik stated he'd not use the move again. Malik will humourously lie and claim that he was referring to his other move "Eternally Sauteed."
Contributed by MightyKombat
The sword that Veigue Lungberg uses when fighting him at Riot Peak is Siegfried's "Requiem" sword from the Soul Calibur games, specifically the Player 1 variant. The Requiem sword that Veigue requests the player to find is the Player 2 variant.
Contributed by MightyKombat
During the events at Warrior's Roost's "Riot Peak" challenge, the player is assisted by a black robed guardian.

Upon completing the Riot Peak Normal class, the player will meet with and be challenged by the guardian, who reveals himself to be Veigue Lungberg, the main character of Tales of Rebirth. Upon defeating him, the player earns the Laevatein sword for Asbel. Veigue will also put in a Request for the player to find a sword named "Requiem" for him.

The player can challenge Veigue again any time they desire after winning or losing to him, although should the player challenge him after winning, they will have to fight him solo with the character they have chosen.

The player can also battle Amber Hearts from Tales of Hearts, and Reala from Tales of Destiny 2, within the bonus dungeon "Zhonecage." When beaten, they give out requests for certain weapons. Once these requests are fulfilled, Amber and Reala can fight alongside Veigue in the final battle of Riot Peak.
Contributed by MightyKombat
Special "Tales series" costumes are available as downloadable content for the game, each costume being based off of characters from different games in the series.

Asbel: Leon Magnus from Tales of Destiny
Sophie: Anise Tatlin from Tales of the Abyss
Cheria: Natalia Luzu Kimlasca Lanvaldear from Tales of the Abyss
Malik: Raven from Tales of Vesperia
Hubert: Flynn Scifo from Tales of Vesperia
Pascal: Harold Berselius from Tales of Destiny 2
Richard: Zelos Wilder from Tales of Symphonia.

In addition, pre-orders and Day One editions of the game included exclusive costumes based off of characters from Tales of Destiny 1 and 2:

Asbel: Kyle Dunamis from Destiny 2
Sophie: Rutee Katrea from Destiny
Richard: Judas from Destiny 2

Wearing any of these costumes changes the battle and victory music to tunes from the current player character's costume's home game.
Contributed by MightyKombat
In one skit, Asbel reads a couple of marriage proposals sent to him, written and sent by "Anise Tatlin" (from Tales of the Abyss) and "Nanaly Fletcher" (from Tales of Destiny 2)
Contributed by MightyKombat
Attachment
In the bottom right of the tower in Sable Izolle is a set of wigs. These wigs appear to reference past "Tales of" characters. From left to right, they resemble Cress Alvein (Tales of Phantasia), Senel Coolidge (Tales of Legendia), Reid Hershel (Tales of Eternia), and Veigue Lungberg (Tales of Rebirth).
Contributed by SOGESNAKE