Mystari's manga / #Mentally unstable(1)

Mihail Meyer (nicknamed "Michel" by his wife) is a half-Japanese doctor. While on the way home with his wife late one night, he nearly runs over a 6-year-old boy playing in the street. Alex is a precocious but endearing child and the son of up-and-coming musician Christopher Adler. Alex and Michel become fast friends, and Michel soon notices Christopher's coldness and neglect towards Alex, though the boy seems to adore him. 10 years later, the widowed Michel has lost touch with the Adler family, but has followed Christopher's career as he rose to become a world-renowned pianist and conductor. One night, after mistakenly stumbling into the gay red-light district, he spots a boy who looks like Alex hanging out with a couple of rowdy-looking guys and gives chase...