Maybe it's just me or this is just an another time paradox situation here.
MC got turned down by his GF,
He got 'Final Destinationed',
timed travelled to his past,
met and confessed to his presumed future GF between the twins,
and all the of a typical harem shenanigan happens,
But in reality,
Classmate black girl is the 'GF' because she strived to be the culmination of all the things MC liked of that 'future GF':
the hair color, facial structure, even the likes and hobbies.