i have finally finished the game, the reason i got stuck is because i didn't go to the some sort of a love hotel that near the oasis, because the game told me the relationship would changewhich make me think i could stayedin the same state relationship as mother and son but as it turns out you have to go the love hotel place to progress further.
I don't know why people keep asking how to beat the final boss which in my ocassion is not that hard, keep leveling up untilthe mc and mother got their last special abillity which is for the mc is called "blade dance or something (i forgor)" and the mother special is "mother beam" once you unlock that, the tower is really really REALLY easy.