Complex sentence: Asano also utilized Punpun's simple look for symbolism, like giving him bull horns to represent Altair, the cowherd star, to symbolize his love triangle as the Summer Triangle with Aiko as Vega and Sachi as Deneb.
Split into simpler sentences: Asano also utilized Punpun's simple look for symbolism, like giving him bull horns to represent Altair, the cowherd star, as part of a summer triangle between him, Aiko, and Sachi as stars. This was meant to represent a love triangle between the trio with Aiko as Vega and Sachi as Deneb.