Hyperion, Themis and Kronos

Hyperion, Themis and Kronos are a trio of antagonists that appear in The Interference, starting in The Interference: Re:coded. They are, as Braig explains, part of Master Xehanort's 'Alex Plan'.

History
The three of them were all part of the canonical future of the Chrono Trigger universe, the time of Chrono Cross. When Alexander Karsath interfered in the game, the additional presence of Edward and Alphonse Elric caused an alteration in the game's story that erased the Chrono Cross future from existence, with only the three of them escaping. The three of them have an important relation to a figure they refer to as Sister, for whom they are searching, and all three recognise Lucca.

At some point, the three of them were contacted by Master Xehanort, who informed them of Alex's warping presence in the worlds and of how they could deal with him. They became the agents of the 'Alex Plan', presumably taking their code-names at this time.

Working Method
So far, none of the members have aggressed Alex directly. Each has travelled to different locations and recovered the Keyblade Armour and Keyblades of Terra, Ventus and Aqua, a trio of Keyblade Wielders from the series prequel Birth by Sleep. All three members use alchemy in order to steal and appropriate the equipment, and each one wields spells from two Chrono Cross elements.

Hyperion
Hyperion appears to be the eldest member of the group, and steals Terra's Armour and Keyblade from the Keyblade Graveyard, his presence alerting the residences of Disney Castle as he does so. He calls somebody (Kronos) on a device similar to a mobile phone to inform them of his success, and then easily defeats King Mickey, Donald and Goofy as they try to intercept him. Later, he reconvenes with his fellows in Fiona's Forest in Guardia.

Hyperion's appearance prior to donning the armour is described as wearing a red-trimmed black robe, and implied to be injured via a limp and a clutched side. His characterisation in his first appearance is confident, as h taunts Mickey's magic and predicts his power will increase; in his second he reveals a dedication to Sister that leaves him in tears when he realises Sister is no longer in Guardia. He uses Red and Black Elements.

Themis
Themis is the sole female of the group. She is assisted in taking Aqua's Armour and Keyblade from the Chamber of Repose by Braig, who in turn uses Lea to help clear the path. When Lea objects, she attacks him, but is stopped by Braig. Afterwards, she calls somebody she refers to as 'brother' (apparently not Kronos, presumably Hyperion) to inform him of her success as she walks away, disappearing to Guardia.

Unlike the others, she only appears after the armour has been donned off-screen; Braig comments that the armour fits her perfectly, but it is known from Kronos' case that all three change shape to fit the armour. Themis is, in comparison to her comrades, perfectly calm. In her second appearance, almost all of her dialogue is dedicated to pointing out the cons of their situations and plans. She uses Blue and Yellow Elements.

Kronos
Kronos is the group's smallest member, who steals Ventus' Armour and Keyblade by travelling to the past, just after Land of Departure was transformed into Castle Oblivion. When Aqua faces him, he removes the helmet to reveal that he looks exactly like Ventus, but with reptilian eyes. According to him, he is apparently now bound to the Armour and would die without it. He produces a portal to travel back to the future, and orders Aqua to reconsider leaving her section of the timeline, before disappearing into it and heading to Guardia.

Kronos, described as black-cloaked like Hyperion, is easily the most ill-tempered and hot-headed of the group. He berates Hyperion on the phone, shows the most open anger about Alexander's interference, and spends the most time taunting Aqua about the plan. Despite his shortcomings, he takes charge of the party during the clearing encounter. He uses Green and White Elements.

Sister
An unknown figure, female, who is mentioned by the others during Across Time and Space. She apparently cloned herself at some point during The Interference III: Wings of Time, and the group's members are searching for her. She is mentioned to possess a great amount of power, and the ability to transport herself to other worlds, though apparently she is not powerful enough to travel to the real world.

These traits heavily imply that Sister's identity is that of Kid from Chrono Cross. Kid is a clone of Schala, the princess of Zeal from 12000BC, who had extensive magical abilities. In the Chrono Trigger continuity, Schala travels through a dimensional vortex to become an element of the Dream Devourer, a version of Lavos. Before her mind was consumed, she cloned herself to create Kid, and sent her to the very near future of Guardia, where she was found by Lucca, who raised her.

Name origin
Hyperion, Themis, and Kronos all take their names from a member of the Titans, the second generation of Greek deities who were born of Gaia and Ouranos, the personification of the Earth and Sky:
 * Hyperion (Ὑπερίων) was the progenitor of Helios, Selene, and Eos. In later writings, he is referred to as the 'God of Watchfulness, Wisdom and the Light', and he was associated with light, the sun and the day. In many texts and translations, he is confused with Helios due to being referenced as the sun god.
 * Themis (Θέμις) was the personification of natural law and custom, her name meaning 'divine law'. She was an Oracle of Delphi and was able to divine the future as well as the difference between truth and fiction. She is said to have sired both the Horae, goddesses of time and the seasons, and, depending on the myth, the Moirai, the Fates. Themis's daughter Dikē, the personification of moral justice, was adopted into Roman mythology as Justitia, and both have statues outside of courthouses around the world.
 * Kronos (Κρόνος) was the leader of the Titans in the overthrow and murder of Ouranos, and was associated with the harvest. Prophesied to be murdered by his own children, he ate his first five offspring until he was tricked into mistaking a swaddled rock for his sixth, Zeus, who rescued his siblings and began the Titanomachy. In Roman mythology, he is conflated with Saturn, brother to Janus.