Sung enlisted on 7 June 2005, for his mandatory military service. Though he initially enlisted as an ordinary soldier, the Military Manpower Administration transferred him to the military promotion ("entertainers") unit in February 2006, for which he served as "public ambassador of military affairs". He was discharged on 6 June 2007. 2008–2014: Comeback and lead roles He made his comeback in the medical drama New Heart (2007–08), playing a cardiothoracic surgery resident. During a scene where his character cries after failing to save the life of a former comfort woman, Ji Sung said he thought of his maternal grandmother who'd recently died, remembering that she'd told him her only pleasure was watching him in reruns of All In. Contrary to his cheeky, playful character, Ji Sung said that he's taciturn and shy in real life, but that the drama made him find a different side of himself. He then made an extended cameo as the sophisticated right-hand man of the mob boss in action noir Fate (2008). In 2009, Ji Sung collaborated again with writer Choi Wan-kyu and director Yoo Chul-yong of All In in the revenge drama Swallow the Sun, adapted from the novel by Kang Chul-hwa, and shot on location in Jeju Island, Las Vegas and South Africa. Ji Sung trained hard to play the tough, strong-willed protagonist who goes to prison for his boss and later becomes involved in the city development of Jeju. In February 2010, he signed with a new management agency, Namoo Actors. Several months later, he played another historical character in Kim Su-ro, The Iron King, as the titular founder of Geumgwan Gaya. In 2011, Ji Sung starred alongside Yum Jung-ah in Royal Family, about the power plays within a chaebol family. Later that year, he was cast in the workplace romantic comedy Protect the Boss. In a departure from his usual serious roles, Ji Sung played a dorky man-child with a panic disorder, who matures and learns to run his father's business after meeting a feisty secretary (played by Choi Kang-hee). From 2012 to 2013, Ji Sung played a gifted seer/geomancer in The Great Seer. His fictional character becomes a "kingmaker" to Yi Seong-gye (played by Ji Jin-hee), the general who leads the overthrow of Goryeo and establishes the Joseon Dynasty, becoming its first king Taejo. In late 2012, he starred in adult romantic comedy My PS Partner, playing an aspiring singer-songwriter