Question: Who sings in the band Tokio Hotel, Bill Kaulitz, Cristina Scabbia or both?

<P0-S0> I'm Not OK is the debut EP by the German rock band Tokio Hotel's lead singer, Bill Kaulitz , and was released through iTunes on May 20, 2016 under the moniker Billy. <P0-S1>  It contains 5 songs. <P0-S2>  The official artwork was designed by German designer Andrew Brawl, who is also a good friend of Billy. <P0-S3>  The EP leaked on the Internet in April, nearly a month before official release due to iTunes music releasing system issues. <SEP> <P1-S0> Bill Kaulitz (born September 1, 1989), also known mononymously as Billy (stylized as BILLY) for his solo act, is a German singer, songwriter, voice actor, designer, and model. <P1-S1>  He is best known for his work from 2001 to the present as the lead singer of the band Tokio Hotel. <SEP> <P2-S0> The discography of Tokio Hotel, a German rock group, consists of four studio albums, two live albums, one EP, one compilation album, seventeen singles, twenty-one music videos, and five video albums. <P2-S1>  Tokio Hotel was formed in 2001 in Magdeburg, Germany, by singer Bill Kaulitz, guitarist Tom Kaulitz, drummer Gustav Schäfer and bassist Georg Listing. <P2-S2>  The group's debut single, "Durch den Monsun", entered the German singles chart at Number 15 on 20 August 2005, and reached Number 1 the following week. <P2-S3>  It also reached Number 1 on the Austrian singles chart. <P2-S4>  It was followed up with the single "Schrei", which failed to match the success of "Durch den Monsun"; its highest chart position was Number 3 in Austria. <P2-S5>  The band released their debut album, "Schrei", on 19 September 2005. <P2-S6>  It topped the charts in Germany and Austria, and was certified Platinum by the German and Austrian affiliates of the International Federation of the Phonographic Industry (IFPI) and by the Syndicat National de l'Édition Phonographique (SNEP) in France. <P2-S7>  In 2006, a third and fourth single, "Rette mich" and "Der letzte Tag", were released; both reached Number 1 in Germany and Austria. <P2-S8>  The lead single from Tokio Hotel's second album, "Zimmer 483", was "Übers Ende der Welt", released on 26 January 2007. <P2-S9>  It became Tokio Hotel's fourth single to have reached Number 1 on the German and Austrian charts. <P2-S10>  "Zimmer 483" was released on 23 February 2007, and reached the top spot on the German albums chart. <P2-S11>  The album's second single, "Spring nicht", was released on 7 April, charting at Number 3 in Germany, 7 in Austria, and 21 in Switzerland. <P2-S12>  "Zimmer 483" was certified gold in three countries. <SEP> <P3-S0>  She used to write an advice column in the popular rock magazine "Revolver", alongside musician Vinnie Paul. <P3-S1>  Scabbia is featured in a Megadeth song "À Tout le Monde (Set Me Free)". <P3-S2> Cristina Adriana Chiara Scabbia (] ; born 6 June 1972) is an Italian singer and lyricist, best known as one of the two vocalists in the Italian Gothic metal band Lacuna Coil. <P3-S3>  She also featured on "The Theory of Everything", an album from Arjen Anthony Lucassen's Ayreon project, with which she is cast as the Mother. <P3-S4>  She is also the featured artist in the Apocalyptica song "S.O.S. (Anything But Love)" and another version of the Alter Bridge song "Watch Over You". <P3-S5>  Her highest note ever hit is claimed to be an A7. <P3-S6>  Scabbia performed a duet with the Italian ex-singer of Linea 77 Emiliano Audisio on the track "Beautiful Lie" to be part of the soundtrack for the 2013 Italian film "Passione sinistra".