In this episode, Ami and Taiga agree to a sports competition. The competition is for a fifty meter swimming races. (Which does not seem possible, since Taiga does not swim all that well.) If Ami wins, she gets to take Ryuji to her vacation home.
Later, a note is being passed around the class. The subject is the contest, and everyone has an opinion. There is some betting, in which Ami is heavily favored since Taiga cannot swim. Ryuji immediately passes the note to Taiga. (Her reaction causes the entire class to flinch, which the oblivious teacher asks her if she wants to try to solve the math problem he put up on the board.)
We next see Ryuji attempting to teach Taiga to swim. (She is not doing very well, partly because Kitamura is also at the pool and she feels very self-conscious around him.) The scene shifts to much later, with Ryuji getting ready to make dinner. Taiga is pretending to swim on the floor. They argue about training, and the dinner menu. (Taiga wants meat and there is a definite absence of it for this particular menu.)
We get a brief training montage that resolves to a rainy day. Taiga is extremely disappointed, but Kitamura provides Taiga and Ryuji with tickets for a public pool. He also states that he is betting on Taiga winning, and provides Taiga with a pep talk.
Later, Ryuji and Ami have a chat. Ryuji is annoyed by the way Ami keeps provoking Taiga. Ami thinks that Taiga is cute when she is jealous. Ryuji denies that Taiga is jealous and states that Taiga is merely annoyed with Ami. The word “idiot” is passed back and forth several times, but this is a friendly conversation. Ryuji states that he does not believe that Ami honestly intends to invite him over to her vacation home but Ami states that she was serious about inviting him, because she feels that she and Ryuji are compatible. Ryuji is dumbfounded by this, then annoyed because it is clear she is teasing him. He tells her to stop teasing people, advice she chooses not to accept.
Next, Midori reveals that she knows that Ryuji was the one who “super-sized” Taiga’s swimsuit. We see that she suspects that the relationship between Ryuji and Taiga is much closer than either will admit to, though she says nothing overtly. Instead, she states that Ryuji being so helpful is a great thing, and that she “trusts” Ryuji to take care of Taiga. (Ryuji probably assumes Minori is talking about the swim meet.)
There is some more practicing later, when Ryuji and Taiga go to the public pool. Ryuji discovers that Taiga has a powerful kick, and might actually have a chance of winning. Ryuji tells Taiga this. She is at first skeptical, but slowly gains confidence. Unfortunately, it starts raining again. They talk about the competition and practicing, though Ryuji misses something very important during the conversation. Taiga becomes upset, and yells at him. Ryuji yells back, mostly because he is confused about why Taiga is upset with him. (Later, Ryuji’s mom attempts to offer some motherly, if somewhat tipsy advice, but falls asleep.)
The day of the competition, Ryuji gives her a bento, and tells her that he wants her to win. Taiga takes the bento, but apparently is not willing to forgive him just yet. The scene shifts to the pool. Two of Ryuji’s classmates give him a hard time about the competition. (They would prefer that they were the ones Ami was interested in, and resent him a great deal. It is interesting that since the initial encounter with Taiga and Ami coming to the school that people seem much less inclined to treat Ryuji like a dangerous delinquent.)
After a long wait, Taiga appears for the competition. She is wearing an inner tube, water wings and various other floatation devices. To get an additional advantage, Taiga tears off the top of Ami’s bikini and takes off at full speed.
(Ami really should have known better. Never wear something that easy to sabotage to a swimming competition with the Palmtop Tiger.)
Ami eventually recovers her top and takes off after Taiga. Taiga has a huge lead on Ami, but gets a cramp. Ryuji dives in after Taiga to help her. Taiga is extremely upset because the person she had wanted to win this meet for had been Ryuji. (Ryuji looks completely stunned when he hears this.) Ryuji encourages her and she takes off swimming again. Then several boys are thrown into the pool and Ryuji gets clobbered. Taiga immediately goes to his rescue, and loses the race. (She also yells at everyone for being more interested in Ami’s bikini than the fact Ryuji had been drowning and declares that Ryuji is “hers.”)
Ami’s “win” is not decisive however. Taiga insists on going to the vacation home as well, since Ryuji takes care of her daily needs. Ami is not really willing to have Taiga come along, but Kitamura gently states that this would be a good idea. Ami decides to tease Taiga for being worried about Ryuji, but Taiga is more than willing to admit that she is concerned for Ryuji. (After all, Ryuji is her “dog” and she is a responsible pet owner.)
So, the end result is that all five of them are going to Ami’s vacation home.