Earphone Jack grants its users long, controllable earlobes that work like headphone cables.
Kyoka's earlobes are shaped like jacks at their ends, allowing her to plug them into a variety of objects. Those earlobes can further channel the vibrations of Kyoka's own heartbeats, dealing internal damage to said objects.
Moreover, Kyoka is able to catch faint sounds through her jacks even across extremely thick walls, making her excellent at scouting work. It is possible, however, to mislead her by somehow generating multiple sources of noise to mask the ones she's trying to detect.
Kyoka's earlobes can stretch up to 6 meters, and the radius of detectable sound is 12 meters. They are sturdy enough to easily pierce hard materials like concrete and able to act as additional limbs due to their prehensile nature, with Kyoka being capable of picking up small objects with them.
It's unknown if Mika has access to all aforementioned abilities displayed by her daughter.
Like any other part of her body, however, the Earphone Jacks are susceptible to damage and may suffer from overuse, evidenced when Kyoka's ears began to bleed from using her Quirk too much in a short time frame during the First Term Final Exam.
Kyoka uses her Quirk mostly for spying or support, making use of her jacks to detect vibrations caused by enemy movement. For offense, Earphone Jack can act as a sort of whip, with Kyoka using her jacks to shock targets with vibrations.
Kyoka can plug the jacks into the boots of her hero costume, which have speakers that allow her to shoot a concentrated blast of sound from her heartbeats in a specific direction. This technique, however, can be countered with a louder, opposing source of sound, such as Present Mic's Voice Quirk. Earphone Jack is able to emulate actual headphones, evidenced by Kyoka plugging her jacks into electronic devices in order to listen to audio in private.
Named Super Moves
- Heartbeat Fuzz (ハートビートファズ Hātobīto Fazu?): Using special sound-amplifying items located on her forearms, Kyoka plugs her jacks into those amplifiers and slams them onto the floor, channeling a powerful heartbeat that causes the ground to shatter due to the enhanced vibrations.
- Heartbeat Surround (ハートビートサラウンド Hātobīto Saraundo?): Using the same sound-amplifying items from her Heartbeat Fuzz technique, Kyoka uses her jacks to remove the equipment pieces from her wrists and aim them towards a target, channeling a loud heartbeat that ignores conventional defenses and incapacitates foes.
- Horikoshi mentions that Kyoka's Quirk is possibly the first Quirk he came up with, way before he even started planning My Hero Academia.
- This is the first Quirk, other than One For All, that is shown to be used by multiple people, those being Kyoka and her mother, Mika.
- However, Todoroki's quirk is identical to his parents.