Rhythm

Rhythm is a Digimon in the form of a human, and appears in Digimon Savers: Ultimate Power! Activate Burst Mode!!. She first appears when the three main Digimon of the series Agumon, Gaomon and Lalamon, are considering what to do now their partners are held captive. She looks at them for a brief moment and then gets chased by a group of Goblimon and an Ogremon.

After the trio assist and save her, they become friends she assists them in trying to stop Argomon.

Later on, she also helps Marcus give ShineGreymon power to enter Burst Mode. After Argomon's defeat, she returns to the Digital World with Argomon's egg, after promising Agumon that they will meet again.

Throughout the movie, interactions between herself and Agumon would imply a romantic attraction. This is confirmed at the end as she explicitly says after kissing Agumon goodbye that she loves him

Trivia
The アルゴ from Argomon's name and リズム from Rhythm's together spell "Algorithm" (アルゴリズム).

The first time the protagonist Digimon introduce themselves is spurred by Rhythm referring to Agumon as "Mr. Frog"