```json
{
  "no": ["no"],
  "yes": ["yes"]
}
```

Based on the given information, the feature "default" represents whether the client has any credit in default. From the analysis, we can see that for the target class "no" (clients who did not subscribe to a term deposit), the feature value for default is only "no". On the other hand, for the target class "yes" (clients who subscribed to a term deposit), the feature value for default is only "yes". Therefore, the possible values of the feature "default" for each target class are as follows:

- Target class "no": ["no"]
- Target class "yes": ["yes"]