"Hakai" (romanization) literally means "destruction", which is a key component in the archetype's playing style. "Unchained" instead references the archetype's design, being prisoned oni who are unchaining themselves from their shackles.
The archetype focuses on breaking their opponent's board, albeit through a limited number of ways. It heavily relies on interaction during the enemy's turn, in order to disrupt plays through utilizing their opponent's own Monster cards for its main gimmick, which is climbing a set of Link Monsters from -2 to -4.
Their main strategy revolves around destroying their own cards with the ultimate goal to summon Unchained Soul of Disaster, as the core gameplay condition.
"Unchained Soul" is a sub-archetype which focuses on Link Summoning using the opponent's monsters, as its main strategy. This allows them to climb into its powerful Link -4 monster, Unchained Abomination, while having preserved its own resources and simultaneously clearing the enemy's board bit by bit.
Despite "Abomination" not being a win condition by itself, reaching it opens the door to a plethora of destruction effects that can easily rid the opponent of their entire board.
"Abomination's" key weakness is a lack of self-protection or floating effect, like the rest of the deck has. That makes it necessary to reduce the enemy's resources low enough during the turn "Abomination" is summoned, so that the deck can leverage its lead and establish enough recovery options or extenders.
As prior to reaching "Abomination" the deck has no more than single removal effects, it should usually be aided by cards which can utilize more destruction and disruption.
Coupling the deck with more flexible archetypes is also a good idea to make up for Unchained's core weakness, which is protection for either destruction itself or, even worse, targetability.