Code Lyoko — Episode 17: XANA's Kiss

You are watching the episode XANA's Kiss Xana creates a ghost called a polymorphic specter, that can change its shape or form at will and doesn't need to possess a host, then uses it to drive a wedge between the group by having it kiss people while disguised as them. At the end of the episode Aelita kisses Jeremy to see how he'll react. He (predictably) freezes up.