The given question presents a series of characters: "キこくけき". The correct answer is "ki" because it is the last character in the series. The characters are arranged in the order of the Japanese syllabary, known as "gojūon," which starts with "a" and ends with "n." In this case, "ki" is the fourth character in the series, following "ko" and "ku" and preceding "ke." Therefore, "ki" is the logical continuation of the series.