Utsuroid

Utsuroids are the monsters of the day in Roaring❤ Hearts Pretty Cure. They are formed by removing a victim's Roaring Spark, the embodiment of their emotions, dreams, and willpower, and blackening it, causing the victim to transform into an Utsuroid. Those who are experiencing particularly strong emotions are typically singled out as targets, as stronger emotions produce brighter Roaring Sparks, which make for more powerful Utsuroids. However, this is a double-edged tactic, as this also causes the Utsuroid to release more Rainbow Energy - the source of the Rainbow Melody - when purified, aiding Pretty Cure in their mission. Their name comes from a portmanteau of "utsuro", the Japanese word for "empty", and "-roid" meaning "individual".

Description
Each Utsuroid takes a form inspired by an aspect of the victim's personality and is characterized by their empty gold eyes, parts of their form being tainted by or outright comprised of a dark substance and the presence of a gem on their body, its color dependent on who summoned it (dark orange for Agate, dark blue for Tourmaline, and silver for Selenite). Said gems serve as the power sources of an Utsuroid, causing them to suffer a drop in power if damaged and shattering completely when the Utsuroid is purified. The Utsuroids summoned by the Void Triad also possess a level of the victim's consciousness and emotions, albeit usually exagerrated in some way. In certain cases, it is possible to impede their actions by appealing to the victim.

Once summoned, an Utsuroid has one prime directive - to generate negative energy, both on their own and by affecting the Roaring Sparks of civilians in the area, providing Sardonyx with a means of restoring her lost powers. If left unchecked, an Utsuroid's influence could lead to the Roaring Sparks of nearby civilains being suprressed, creating more Utsuroids and setting off a dangerous chain reaction. Luckily, the average Utsuroid is not powerful enough to blacken the Roaring Sparks of others quickly enough for it to become a significant problem, giving Pretty Cure ample time to defeat it and protect its victims. If left alone, the Utsuroid will eventually stop moving and revert to its original form; however, the victim is left as an empty shell due to the (apparently) permanent blackening of their Roaring Spark.

Sardonyx can directly transform people into Utsuroids with more fast-acting suppression abilities. Although these variants are not bound by many of the restrictions of those summoned by the Void Triad, as they lack a weak point or any remnants of the victim's personality, and can turn victims into more Utsuroids simply by coming into contact with them, they do not release sufficient amounts of negative energy.

Staring from episode nine, the Utsuroids the Void Triad summons are powered up, neccesitating Pretty Cure to unlock their Melody Arms and eventually, their powered-up combined attack in order to defeat them. This increase in power is denoted by gold trim surrounding the gems on their forms.

Trivia

 * Utsuroids are inspired not only by the Desertians from Heartcatch Precure but by the Phages from Sailor Moon Sailor Stars, with many aspects of their creation being a deliberate shout-out to the latter.