Kira is the main villain of the fourth arc of JoJo's Bizarre Adventure, Diamond is Unbreakable (also known as Diamond Is Not Crash). He is DLC in JoJo's Bizarre Adventure: All Star Battle.
Kira is a typical Japanese salaryman in his every day life. He is exceptionally intelligent and talented but he wishes for a simple life and avoids attention. In high school, he participated in many competitions, but he goes out of his way to win third place so that he wouldn't stand out. If Kira attracts attention in any way, he would resort to extreme lengths in order to redirect attention away from himself.
Kira is handsome and has many female admirers, though the only "women" he shows interest in are the decapitated hands of his female victims, which he keeps as "girlfriends". Kira developed his fetish for the female hand when he first saw the painting of the Mona Lisa. His Stand, Killer Queen, has the power to turn its target into an explosive, and he uses this to vaporize all of his victims' remains, sans the hands. He has terrorized the town of Morioh for over a decade.
Kira collects his fingernail cuttings as a method to divine his luck in continuing his murdering spree and keeps them in jars divided by month. If his fingernail cuttings have increased since the previous month, it would mean that his luck for the following month would be better.
Kira started his murdering spree by viciously stabbing his victims with a knife, and his first victims were Reimi Sugimoto and her family and her dog, Arnold. His strong desire to leave no evidence behind eventually led to the awakening of his Stand, Killer Queen. So effective was Killer Queen in Kira's activities that the police could only believe that the victims had simply disappeared.
Diamond is Unbreakable
Kira was first seen with a woman's hand that he hid in a sandwich bag. Shigekiyo Yangu accidentally swapped his sandwich bag with Kira's. Kira chased Shigekiyo to Josuke's high school in order to keep his identity secret. Kira reclaimed the hand and vaporized Shigekiyo using Killer Queen, the first demonstration of Killer Queen's ability.
Kira was later seen again when Jotaro and Koichi were investigating a lead that led them to a shop where Kira sent his coat for repair. Kira sent Killer Queen's second ability, Sheer Heart Attack to attack them. Koichi's Stand, Echoes evolved into Echoes Act 3 and used it to disable Sheer Heart Attack. Kira then decided to cut of his hand to free himself from the effect of Echoes' ability and confronted them in an attempt to finish them off. Kira fled and met Aya Tsuji and made her change his physical appearance to that of Kosaku Kawajiri using her Stand, Cinderella. Kira then successfully stalled Jotaro's hunt for him for an extended period of time.
Kira's father, Yoshihiro Kira, delivered an arrow to Kira, allowing Killer Queen to gain a new ability, Bites the Dust. Kira also acquired a potted plant Stand-wielder, Stray Cat. Kira decided to use Killer Queen's new ability to finish off Josuke and his allies.
Kira first used Bites the Dust on Kosaku's son, Hayato and made him the bait to kill Josuke and his allies. Hayato quickly learned the mechanics behind Bites the Dust and exposed Kira's identity to Josuke. Realizing that he no longer has a target to use Bites the Dust on, Kira decided to engaged Josuke in a fight.
Kira utilized Stray Cat's ability to create and control air bubbles and turned the bubbles into explosives. Josuke realized that Yoshihiro was giving directions to Kira to control the bubbles via a walkie-talkie and Josuke snatched the walkie-talkie and gave directions Kira to kill Yoshihiro. Josuke then defeated Kira and his punch sent Kira into the streets.
Kira attempted to use Bites the Dust on a pedestrian but Koichi had frozen Kira's hand, preventing him from using Bites the Dust. Jotaro then approached Kira and pummeled him with Star Platinum. Kira later found himself with Reimi. Reimi recognized Kira and showed him her back. Reimi's dog then tricked Kira into sending him into being dragged into the next world.
Killer Queen's base ability is to turn its target into an explosive. The target will explode, leaving no trace behind. Kira may set the target to explode on contact or to detonate at his choosing.
Sheer Heart Attack
Killer Queen's second ability is a remote Stand called Sheer Heart Attack. It is housed in Killer Queen's left hand and it represents Killer Queen's left hand. Sheer Heart Attack is an invincible bomb with tank-threads that will approach the warmest object in the vicinity and cause it to explode. Unlike true remote Stands, any effect that is inflicted upon Sheer Heart Attack is inflicted upon Killer Queen, and by extension, Kira's left hand.
Bites the Dust
Also known as Another One Bites the Dust. Bites the Dust is activated by Kira telling someone all his secrets, then Killer Queen will embed itself on the person, making him the bait. If anyone tries to demand that information from the bait, Bites the Dust will kill the person demanding the information. A time loop is then created, forcing the bait to live the day's events again; but during every time loop, Bites the Dust will kill the same person as well as any additional people that had been killed by Bites the Dust before. Kira will allow this loop to occur repeatedly until all his targets have been killed.
While Bites the Dust is active, only Kira and the bait can perceive the full effect of Bites the Dust and remember all the time loop events.
Kira can call off Bites the Dust at any given time. Also, Hayato noted that Bites the Dust can only be used on non Stand-wielders.