Male Ritsuka's version of the Polar Chaldea Uniform worn as a Mystic Code in Fate/Grand Order, introduced into the story during the Russian Lostbelt to help the protagonist survive in severely cold conditions.
For Female Ritsuka's version, see Fujimaru Ritsuka (female) (Polar Chaldea Uniform).
This tag implicates fujimaru_ritsuka_(male) (learn more).