WARNING: The following contains spoilers for Episode 4 of SSSS.Dynazenon, "What is This Thumping Heart?," now streaming on Funimation.
The relationship between Yomogi and Yume has been a huge focal point throughout SSSS.Dynazenon's first few episodes. While the show has teased romantic development between them before, Yomogi’s concerned curiosity has finally developed into an infatuation with Yume by Episode 4. Meanwhile, he suffers from a cold, becomes increasingly distracted, and obsesses over minor details and his own assumptions. Even so, he may have won Yume over.
The latest episode begins with more training for the Dynazenon pilots. While practicing his balance and control with Dyna Soldier, Yomogi notices that Yume is not present. His dejection results in a botched practice session and an angry Gauma, who chastises Yomogi for his lack of focus. Despite the reprimand, Yomogi asks Gauma about Yume’s absence.
Gauma tells Yomogi that Yume is out meeting someone and this incomplete fact plagues Yomogi’s mind for the majority of Episode 4. Yume is revealed to be meeting a former student and chorus club member who might have information about her sister. However, Yomogi is not aware and remembers Yume’s bad habit from the first episode -- she would ask guys out and never arrive. This included Yomogi, who was left in the rain. So, he resigns to not asking about it despite his desire to know more about her.
At work, Yomogi continues to zone out, which leads to his manager once again teasing him. As she pesters him, Yomogi finally admits out loud that he may have a crush on Yume. Shortly after, Yomogi starts showing symptoms of a cold: at first, a sneeze, and then quickly escalating until Yomogi is bedridden.
During the following training session, Gauma instructs Yume to check on Yomogi since he believes the illness is her fault. Yume’s visit provides the perfect opportunity for more bonding and the chance for Yomogi to ask about her meeting. The clarity puts him at ease just before another kaiju attack.
Initially, Yume leaves without Yomogi to go fight the kaiju, but the team is desperately outmatched without their Dyna Soldier pilot. Yomogi takes the initiative to contact Yume and gets in the fight. He is still sick with a fever and body aches but decides to fight, regardless.
Episode 4 of SSSS.Dynazenon uses Yomogi’s cold as an illustrative metaphor for his feelings for Yume. As he announces his crush for the first time, the cold announces itself. Over time it worsens as he continuously contemplates asking her on a date, the nature of her meeting and his own feelings. He is only alleviated after he does something about his feelings.
After the fight is won, and Yume and Yomogi are flying back home in Dyna Wing, Yomogi doesn’t ask Yume on a date, but he does finally act on his feelings -- asking Yume if he can join her the next time she meets someone with information about her sister. Incidentally, Yume sneezes as Yomogi proclaims he wants to know more about her. The next day, Yomogi is back in school and perfectly fine, but Yume is at home bedridden.
Her final line before the credits is "I guess I caught it," which could be a double entendre. While she definitely caught Yomogi’s cold, she may have also "caught" feelings for Yomogi. Although he was sick, Yomogi still came to fight and protect his city, reaffirming a shared value with Yume established in Episode 2. This value is, in turn, shown to be incredibly deep to Yume, possibly as a result of her sister’s death. Yomogi then takes initiative to show interest and concern for her and her sister when he asks to join in with the hunt for information on her. That’s when she sneezes, and given how the cold mirrored Yomogi's internal desires, there’s a good chance this crush could be reciprocal.