Don't mistake it Sparda already knew his father was a s*um. When he got the headache it restored his memories along with his powers. He also awakened his sacred gear but didn't attacked Rizevim because he knew if he attacked now he will lose because GATE OF BABYLON was his sacred gear and Rizevim can cancel sacred gear. And he was not sure if he would be able to defeat Rizevim with his VECTOR MANIPULATION. He first needed to control all his master all his powers. With instant mastery it won't be hard but he didn't use his powers even a single time.
Sparda when regained his memories he was really shocked to find that he was twin brother of Vali but he quickly calmed down since he was no a kid anymore atleat not mentally. Seeing his reaction Rizevim was really shocked that he didn't attack him to did anything noticeable. He knew Sparda was more powerful than Vali so he didn't lament on it. He thought he was not so attached with his father. But Sparda was thinking now that he had to get more strong. He knew that ABSOLUTE STRENGTH is everything nothing stands against ABSOLUTE STRENGTH.
Rizevim: Sparda its really disappointing that you didn't awaken your sacred gear. But I guess my fool of a son was not enough stimulus for you.
Sparda: It's not that grandpa I just didn't get a reaction like brother.
Rizevim: I see…. Then it will be quite difficult for you from now on as your brother has awakened his sacred gear DIVINE DIVIDING the sparring sessions will get more difficult for you.
Sparda: If it became easy it won't be fun. Grandpa what was the ability you used to cancel the sacred gear of brother???
Sparda asked his grandfather with stars in his eyes. Hearing his 1st reply Rizevim got shocked but quickly put it back in his head as his genius grandson was enthusiastic about his ability.
Rizevim: It's my ability called SACRED GEAR CANCELLOR. Do you want to learn it??
Sparda: Yes when will you teach me should I get ready now??
He asked again with stars in his eyes.
Rizevim: No not now. You must be tired today. Take your brother to his room. I will show you tomorrow.
Sparda got a downcast face but still complied. He carried his brother to his room then he went to his own room. He got on bed but immediately didn't wnet to sleep and started thinking what he should be doing next. It's not that Sparda hated Vali but also didn't liked him much. In his previous life he already thought that Vali was nothing without his sacred gear. He admired him but also didn't liked him that much at the same time. Sparda hated ISSEI to his core because every girl in the story was throwing herself to him but he just kept shouting OPPAI and OPPAI and did nothing. He really felt sorry for DDRAIG. He was thinking all this when suddenly…
[INSTALLING SYSTEM- 1%...3%...7%....13%...19%...37%...56%...73%...85%...93%...100%]
[STARTING SYSTEM!! HELLO HOST]
Sparda:
[ALL OF YOURS POWERS GIVEN BY GOD WAS SEALED UPTO THIS POINT SO IT TOOK ME SOME TIME]
[WHAT CAN I DO FOR YOU HOST]
Sparda:
[I HAVE 5 FUNCTIONS]
[STATUS]
[SKILLS]
[MISSIONS]
[SHOP]
[INVENTORY]
Sparda:
[OPENING STATUS].....