Lord Naarayana or Lord Vishnu is the only original and the first living being existing even before the existence of this cosmos or the first created being Lord Brahma! He is the original spirit soul and you know that the spirit soul is an eternal particle and anything other than it is material or perishable, even if it is Lord Brahma who has the supreme life span, he is also afraid of death and is subject to the laws of material universe even though he is in the highest abode of the 14 planetary systems or Satyaloka.
Material universe is a pair of opposites or a dual substance as you can say and it is always in a relative realm. Only the spiritual universe or Vaikuntas, the abode of Lord Vishnu/Lord Naarayana is an absolute realm with no concepts of duality in time or space and is the place of fully realised surrendered souls under the constant and mutual service of Lord Naarayana.
The vivid descriptions of Vaikunta is described here and these are the topics of worthy discussion:Description of the Kingdom of God.
Jaya and Vijaya are the doorkeepers of Lord Vishnu and as such they are sinless souls, as you would expect them to be since they are in the Vaikuntha.
They are ordained to be cursed by the mother earth or Goddess Lakshmi Herself for the pastimes of Lord Naarayanaa for incarnating Himself as Varaaha (Lord Boar) and Lord Narasimha (Man-Lion) and further as Lord Ramachandra and Lord Shri Krishna, enacted through the mind-born sons of Lord Brahma Sanaka, Sanandha, Sanatana and Sanatkumara.
The details are all there in the 3rd Canto Chapters 12-19 of Srimad Bhagavatham.
As such, asuras are a class of living beings who are extremely passionate or in rajas mode, created during the evening twilight hours by Lord Brahma (the entire creation process is explained in Canto 2 and Canto 3 of Srimad Bhagavatham) which is considered inauspicious for doing anything other than auspicious religious activities because of the pre-dominance of Lord Rudra (Bhoothanaath) and his disciples, ghosts and hobgloblins during that time(that’s why, the concept of tri-kala sandhyavandhana worship of the sun and veda-maatha Gayatri during this period to counteract this influence and pacify Lord Rudra is prescribed) as even time is governed by the mode of material nature and appropriate acts are to be performed only at the appropriate time!
Asuras were existing at all points in the yuga cycle along with other created beings. Matsya or fish incarnation was before Varaha and Lord Vishnu as Matsya killed the asura or demon Hayagriva to restore the Vedas that this demon stole from Lord Brahma while the process of pralaya was taking place and Lord Brahma was worried about the next creation process after he lost the Vedas to this asura!
Asuras are as such a class of beings with predominance of the base modes of material nature – rajas and tamas. They have no discrimination of right/wrong or knowledge of reality, practising atheism/pseudo religion principles, they have strong sense of the bodily concepts of life – I/mine/material possessions there of – predomination of the mode of false ego deludes their mind.
They actually need not have powerful bodily features and physical dominance as described about their characteristics in the Puranas/Ithihasas. The strong passion to lord it over material nature with a strong sense of duality, superiority, cunningness and crookedness in exploiting any living creature to one’s own advantage is enough to classify one as a asura or demon!
You may note the significance of the word Kripanah in these regard as i depicted these class of beings: