Mushrooms of Love

The  are a magical item that appears only in the anime continuity, in the episode "Let's Go to the Mushroom Temple".

The Mushrooms of Love grow in a small region somewhere in the Mountains of Japan, near the episode's titular temple. If cooked and eaten, as the name suggests, they act as a love potion, inducing a deep romantic attraction and a tendency towards saccharine displays of affection in those who have succumbed.

It's a little unclear how they work, but presumably any individuals who eat the mushrooms at the same time succumb; this is why only Ranma Saotome and Akane Tendo succumbed to their effects, as only Ranma's bowl contained them and Akane stole some from his bowl.

What is clear is that the love potion effect is very strong, and grows increasingly stronger. Unless an antidote mushroom from the "Mushroom God" at the sister-shrine is eaten within a few hours, the effects of the mushrooms become permanent.