Urd convinces Belldandy to make Valentine's chocolate for Keiichi and plans to interfere to get them together, but Mara has a similar idea with chocolate of her own.
Summary
Urd watches TV and learns about how people on Earth celebrate Valentine's Day and supposedly, women have to give men chocolate, or else that man will be considered a loser. She goes to Belldandy and tells her about this, which makes Belldandy feel guilty about having never given Keiichi any Valentine's chocolate, so she plans to make enough chocolate to cover both this year's and last year's quota.
A demon with a built-in camera records their conversation and reports back to Mara, who downloads the camera footage via its tail. She plans on getting back at Keiichi with the help of her new "booster demon".
Urd makes her own chocolate with a sprinkle of love potion to make Keiichi fall head over heels for Belldandy, but she accidentally dumps the entire content's worth. Nonetheless, she imitates Keiichi's voice to distract Belldandy and swaps her sister's chocolate for her own.
Mara sneaks up right outside the Temple and instructs her octopus-shaped booster demon to switch out Belldandy chocolate for the chocolate that she made herself, but the demon isn't very smart and has to ask what "switching" means. Meanwhile, Belldandy figures out what Urd had done and demands that she undo the swap. However, by the time they go back to find Urd's chocolate, the booster demons had already swapped it for Mara's chocolate. When they report back to Mara, she breaks up Urd's chocolate, which the booster demons help themselves to.
Belldandy presents Keiichi with chocolate, unaware that it's not actually hers. As soon as Keiichi takes a bite out of it, Mara appears inside the Temple, having bypassed the good luck charms Keiichi had set up to keep her out. Belldandy attacks Mara with a magic attack, but it has no effect on Mara because the booster demons have increased her power. Mara boasts about how Keiichi will in moments succumb to the poison that she had imbued into her chocolate, but for some reason, Keiichi isn't affected at all. It turns out that eating Urd's chocolate earlier has scrambled the booster demons' programming, and now they can only think about consuming more chocolate.
The booster demons turn to Urd holding Belldandy's chocolate and manage to seize it from her, but upon eating it, they become agents of righteousness and turn on Mara, who fires them by knocking them back with demonic energy. Belldandy abhors Mara's behavior toward the creatures she created and attacks her with another blast of magic, which inadvertently gets boosted in power by the booster demons and blows Mara high into the sky.
The booster demons state that they have used all of their life energy in helping to defeat Mara, but Urd combines them into a single, larger creature named Sudaru, who still asks for chocolate from Keiichi.