Italy's "Ooyu wo Hito Wakashi Shiyou" (a.k.a. "Let's boil hot water") mixed with "I'm Yours" by Jason Mraz. Another random experiment. I tried this right after I finished Japan's "version" but I think this one works better. I had to cut a huge part of "I'm Yours" for this to work, that's why it's in the Junk Pile.
I'm not even a fan of Jason Mraz (nor of the original "I'm Yours") but I had this song stuck in my head thanks to my brother who kept humming it for a good couple weeks.
[ Original songs ] ● Vocals: "Ooyu wo Hito Wakashi Shiyou" by Namikawa Daisuke (anime: Axis Powers Hetalia): tempo 131 BPM → 151 BPM ● Instrumental: "I'm Yours" by Jason Mraz: pitch +2