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Sonny was a small Titan that stood 4 meters high and had short messy blond hair and light blue eyes. It had light peachy-colored skin like the other normal Titans and often had a dazed expression.
Sonny displayed typical traits for a Titan of its class. It exhibited little intelligence, appeared to feel no pain when attacked, and ignored a spear driven into its heart because it had a chance to eat Hange Zoë. It lost activity after an hour of sunlight deprivation and Hange described its personality as "introverted".
Sonny presumably first appears when the gate of Trost District is broken by the Colossus Titan and numerous Titans invade the district. However, once the breach is plugged by Eren Yeager, human forces are able to retake the district. Most of the Titans who had entered are killed, but two are taken alive; Hange nicknames them "Sonny" and "Bean". They perform a number of experiments on them including: testing their response to attempts at communication, injury, and sunlight deprivation. They have further tests planned; however, during the night, both test subjects are killed by unknown assailants. Armin Arlert later comes to the conclusion that this was the doing of Annie Leonhart, as he believes that she used Marco Bott's vertical maneuvering equipment to escape suspicion during the investigation of the Titans' murder.
- Hange's nicknames for the two Titans, Sonny and Bean, are direct references to the famous cannibal of the same name, Sawney Bean. However, the former uses an anglicized version of the name.
- In the anime, Hange had two test subject Titans that had died before they captured Sonny and Bean, their names were Chikachironi and Albert. These are also references to cannibals, specifically Andrei Chikatilo and Albert Fish.
- Sonny shares the same voice actor with Franz Kefka in the original version of the anime.