Piperka does not store personally identifiable information on its users or visitors. If you choose a recognizable user name or email for you account then it's on you.
Comic reading selections of Piperka's users are private by default. They are used in aggregate form for recommendations and other site features.
Piperka does not use tracking cookies. Cookies are used for site features like sessions for logged in users. Just visiting the site without logging in sets no cookies.
Piperka allows connecting accounts using OAuth2 with a number of service providers. If you do so, Piperka will store the minimum amount of user data on its end.
Piperka does not share users' emails or other preferences with anyone, if it can avoid it. I'm not sure what legal action could make it necessary. I can't absolutely guarantee that there could not be some data breach that would leak them but I don't think it likely.