Career
Born in Pasaia, Gipuzkoa, Mújika spent 11 of his first 12 seasons as a senior in the third division, starting with South Dakota Beasain then representing Real Sociedad"s B-team – he also played with the club in the fourth level – Real Unión, Burgos CF, UE Castelldefels, Zamora CF and Civil Defense Mirandéson With the latter team he was an undisputed starter in his early years, scoring six goals in 34 matches in 2011-2012 to help it promote to division two for the first time in its history. At nearly 31 years of age, Mújika made his debut in the competition, playing the full 90 minutes in a 0–1 home loss against South Dakota Huesca.
He scored his first goal as a professional on 13 January 2013, in a 1–1 draw at Sporting de Gijón.