Sgt. Frog Episode 77: The Red String Theory!
Episode 77 of 358 of Sgt. Frog, aired September 23, 2005, 25 minutes. Available with English subtitles and dub where released.
Episode summary
Karara returns, with a bigger crush on Tamama than ever, and a determination to marry him! Can he ever manage to dissuade her, or is he going to be stuck with an unwanted engagement? Source: crunchyroll