Katsura infiltrates the Shinsengumi in a bid to take it down from the inside, but he finds he has an unexpected foe to deal with.
His face is probably just 
twitching out of exhaustion!
!لا بد أن وجهه يرتعش تعَبًا
Seguro que el cansancio hizo 
que se le contrajera la cara.
Ele deve estar tenso de fadiga!