[JollyRoero]

The spoilers you've been waiting for provided by @Le Fay

Spoiler for Spoilers:

The first part is Sirzechs being born

And Venelana saying that he will be able to become the strongest

Then it skips to Sirzechs 17 years old

He plays piano and sings with children

Then he is being called by Gremory's servant and attends the party organized by Beelzebub's relative

The relative bullies a child from Orias

He retaliates and hurts Beelzebub's relative

The relative becomes angry and almost kills the one from Orias

Sirzechs protects him, annihilating Beelzebub's attack with power of destruction

Btw, Serafall, Ajuka and Falbium are also present

Maou's descendants are Rizevim, Bidleid Bashalum Beelzebub, Tsufaame Tereaku Leviathan and Something Zereikel Asmodeus

Beelzebub asks Sirzechs to fight him

But Sirzechs can one-shot him and only annihilates Beelzebub's attacks

Beelzebub's special trait is "King of Flies"

After Sirzechs defended effortlessly against Beelzebub's attacks, Beelzebub summoned a giant monster, but this monster's target wasn't Sirzechs himself. For Sirzechs and Ajuka this monster is nothing. Serafall and Ajuka would deal with him. But then they'll show their true power (Sirzechs didn't show his power of destruction until this incident). Sirzechs doesn't want it, because he thinks that he was the cause of this incident. He annihilates monster, but Beelzebub doesn't give up. Then they were about to continue, someone interferes. It's Grayfia. She pulls them apart and then Sirzechs introduces himself to her and asks for her name. Then the scene switches to Venelana and Zeoticus. They talked about the incident earlier and about possible renewal of war between the three great powers. It could lead to the extinction of devils. Venelana also asks Zeoticus which name should they give to a daughter if they had one. Zeoticus answers with "Rias"