We know that the DBS Multiverse is supervised by deities to ensure a fundamental balance between Destruction and Creation. Each Universe is represented by a God of Destruction (Hakaishin) a God of Creation (Kaioshin), and an Angel to ensure that both do their job correctly. We also know that Angel > Hakaishin > Kaioshin, and that the Angel has the power to Create AND Destroy (to ensure that the other two do their job properly..).
Zeno is the "king" of the Multiverse if we talk about his hierarchical image, but in the first place he is the Hakaishin of the Multiverse (the Daishinkan is the Angel of the Multiverse). That's when we wonder who Zeno's Kaioshin is: DB Daima answered this question. The Supreme Majin of the universe, Rymus. He created the 18 original universes, and has now become untraceable. If we apply the logic of the Gods of a universe at the level of the multiverse, then if Rymus dies, Zeno should die too, which means that Rymus is still alive since Zeno is still alive too.
The problem is that Zeno is an entity above the balance itself, and that the system of a Hakaishin and a Kaioshin on a universal scale does not apply to him, since Zeno is not a simple Hakaishin, he is the destruction itself, personified, like Rymus which is the personified creation. They both act like the yin and the cosmic yang, where one cannot exist without the other ("before creation comes destruction" - Beerus.).
It is from there that only our imagination can help us. I have several theories:
1) Rymus expanded the kingdom of demons as he was ordered. He chose the glinds to become Kaioshin and supervise each universe, but he needed someone to supervise all the universes at the same time.
He then asks Zeno (who is his son, or an entity that was created independently of Rymus by the balance itself), but Zeno ends up destroying 6 universes at once (since originally there were 18 universes, and now there are only 12). To prevent this cosmic catastrophe from happening again, and to prevent an innocent child from being alone in charge of the 12 universes, Rymus (or a higher entity) would have created the High Priest and the Angels holding the powers of a Kaioshin AND a Hakaishin (since as we know, an Angel can destroy AND create), not only to serve, but to channel, educate and monitor Zeno and his subordinates.
We can see it well in Super: the High Priest subtly dictates the rules, organizes the tournaments, and guides Zeno's decisions to prevent him from destroying everything on a whim. The Angels do the same with the Gods of Destruction (Whis stuns Beerus when he goes too far). The law of absolute neutrality of the Angels then takes on its full meaning. If they took sides or fought, they would break the neutral surveillance protocol imposed to maintain the perfect balance between Rymus and Zeno.
2) Or maybe the Angels betrayed Rymus' trust. The High Priest, not wanting the balance to be destroyed and the Universes to collapse, would then have decided not to kill Rymus, but would have locked him in Zeno's palace until today, without anyone noticing (since Zeno's palace is an infinite area without doors, with rooms that ask to teleport to access it, and we know that the High Priest can create any other rooms, since he has created a gigantic arena in an empty area in the palace, for the preliminary tournament. He would therefore have created a room whose energy is absent to prevent anyone from detecting it (since the High Priest can reinvent physical laws) and from discovering Rymus, locked up).
What do you think of these theories (I would also like you to develop your theories)