So, I've played this game like in 2021 and I had to play it again as of now, just to beat all three rivals. One of them was easy to beat, two others are hard, but I actually won recently, and also got the medals too.

For the rivals, the A route is easy, while the B and C Route rivals are difficult, but they are all beaten. I used the Lucifer Diablo which is unlocked after beating the Route C rival, in order to beat the Route B boss, just to make them go out of bounds like the Route C boss. I shockingly won like three times on Route B after that, so all 4 cars are unlocked! High-scores and medals are there too.