There are 4 different endings in the game depending on your choices:
1st: Kill Emperor Nuvius in the PRESENT; then take the thrown
2nd: Kill Emperor Nuvius in the PRESENT; go back in time to be with your friends
IMPORTANT: You can see 3 endings in one playthrough. Both ending listed above and only 1 ending listed below. The other achievement/ending you will have to get in NG+
3rd: go to the PAST and kill Prince Nuvius/ then fight the boss Sandman/ then fight the boss Nightmare... doing this gets you the achievement “Hero of Winderia”
4th: go to the PAST and kill Emperor Vol/ then fight the boss Sandman/ then fight the boss Nightmare... doing this gets you the achievement “Savior of Vilete”