Lum goes for a fly and a swim to clear her mind of her recent spats with Ataru, but can not get her mind off the fact that he has never once said "I Love You" to her.
Honestly, I felt that Lum was being ridiculous in this movie. She remained angry at Ataru, despite learning how he had been tricked with that mushroom clone. And then, she starts this whole test, questioning Ataru’s feelings for her, despite all the times where he’s shown to care about her.