the bug occured when you bought all the upgrades before conquering all the girls.
improperly nested if statements caused the ending to be flagged as something you got even though only the 2nd condition was met.
the ending is still fucked and that requires some save editing to fix
(or you can play the game again after redownloading , your choice)
to find the saves go to C:\Users\ (YOU) \AppData\Local\Jigoro
back to ending="0.0000" ot whatever, change the 1 to a 0
then overwrite and enter lux to see the ending.