The 'Not Fair' singer was seen passionately embracing Wade Oates, the 23-year-old guitarist of The Virgins, after bumping into him at the Fuji Rocks festival, which was held in the Japanese city.
An onlooker said:"There was an instant attraction. They were making out all night and didn't care who saw them. Lily seemed very pleased with herself and was glued to his side all night."
However, Lily - who has previously dated Chemical Brothers star Ed Simons, record executive Seb Chew and art dealer Jay Jopling - has no intention of dating Wade as she's happy being commitment free.
A source said: "She's single and enjoying herself. She's too busy to meet up with Wade."
Wade is not the only man Lily has shown a liking for recently.
This week, she expressed her admiration for England cricketers Graham Onions and Andrew 'Freddie' Flintoff.
Lily - who was recently linked to painter and decorator Sam Cooper - wrote on Twitter: "Is Onions married? Anyone? Come on Onions! commentator just described him as 'tall dark haired and pigeon toed' ???? cricket commentary is another world.
"In other news, i think i fancy Graham Onions more than Freddie now. i've heard he goes for days. But Freddie Flintoff is f***ing fit (sic)."