When did Ulrich start liking Yumi?

Ulrich first started liking Yumi when they first met and started sparring in the prequel episodes, X.A.N.A Awakens Parts 1 & 2, but actually ADMITS to himself, Odd, and Jeremy that he likes her in episode 12, Swarming Attack, after Sissy writes him a fake tình yêu letter signed from Yumi.