Vishnu is the enemies of Asuras . Vishnu and Indra together slaughtered innumerable asuras in vedas and deprived them of everything over the universe. Prajapati created Indra as the lord of gods to balance the universe. Asuras were the beings who violated the laws of RTA and were punsihed.
From what we know prajapati created Indra to become the chief of gods.
Taittirīya Brāhmaṇa 2.2.10.1.
- प्रजापतिरिन्द्रमसृजतानुजावरं देवानाम् ।
- तं प्राहिणोत् ।
- परेहि ।
- एतेषां देवानामधिपतिर् एधि इति ।
- "Prajāpati created Indra, the youngest among the gods. He sent him forth, saying: 'Go, become the lord of these gods.'
Indra and Vishnu together defeated the race of asuras
- Ṛgveda 6.69
- उभा जिग्यथुर्न परा जयथे न परा जिग्ये कतरश्चनैनोः ।
- इन्द्रश्च विष्णो यदपस्पृधेथां त्रेधा सहस्रं वि तदैरयेथाम् ॥
- "Both of you have conquered; neither is overcome. Neither of the two has been defeated. When you two, Indra and Viṣṇu, engaged in conflict, you set this threefold thousand in motion."
This mantra is further explained in more detailed fashion in Aitreya Brahmana. Indra and Vishnu together defeated asuras and then Vishnu completely stripped asuras of everything with his three strides Aitareya Brāhmaṇa 6.15 i
- सोऽब्रवीदिन्द्रः — यावदेवायं विष्णुस्त्रिर्विक्रमते तावदस्माकमथ युष्माकमितरदिति ।
- स इमाँल्लोकान् विचक्रमेऽथो वेदानथो वाचम् ।
- तदाहुः किं तत्सहस्रमिति । इमे लोकाः इमे वेदा अथो वागिति ब्रूयात्
- Indra said: 'As much as this Viṣṇu traverses in three strides, so much shall belong to us; the rest shall belong to you(Asuras)
- He (Vishnu )traversed these worlds, then the Vedas, and then speech with his three strides
- Regarding this, they ask: 'What is that thousand?'
- One should answer: 'These worlds, these Vedas, and speech.'"
By his strides Vishnu stripped asuras of everything and devatas controlled dominance over the whole universe including vedas and speech.The three strides here simply don't represent the universe but also includes vedas and speech
Loka — the cosmic worlds.
Veda — the Vedic knowledge.
Vāc — speech itself.