Gintama - Season 5 Episode 2

As Katsura and Kyubei fight for the title of the best transgendered, Shinpachi leaves to find that the Shinsengumi members also suffered a sudden change in their selves; Sogo Okita is the leader from the group and orders him and Toshiro Hijikata, Sagaru Yamazaki to attack the Yorozuya. As the three leave, Hijikata knocks out Yamazaki, as he was faking his change. He and Shinpachi learn that an invasion of parasite aliens is responsible for change to their friends and proceed to destroy them. However, they find problems in the outcome, and both Hijikata and and Shinpachi are knocked out in the process, with Gintoki being actually only person without a parasite.