Ruka Kanae
The argument for a theoretical Ruka win is thematic. Rent-A-Girlfriend is about the difference between rental (fake) and real love. Ruka’s love is the realest thing in the series. It is ugly, inconvenient, and persistent. In many other rom-coms, the girl who fights the hardest wins. In reality, and in this particular manga, the hardest fighter isn’t the right match.
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When she realizes her time is up, she doesn't throw a tantrum. She doesn't sabotage the winner. instead, she accepts reality with a smile, encouraging Fuutarou to be happy. This level of emotional maturity is rare in anime rivals. It cements her not as a "loser," but as a young woman who grew through love. ruka kanae