Tripurasura narrative (Ashtavinayaka sthala-purana)
Tripurasura, born from sage Gritsamada's sneeze, learned the Ganesha mantra from his father and propitiated Ganesha; Ganesha granted him invincibility against all but Shiva. The asura built three flying cities (Tripura) and terrorised devas and earth. On the devas' prayers Shiva launched a campaign; Narada informed him that since Gajanan had empowered the asura, only Gajanan's grace could enable his fall — and Shiva realised that he had omitted to recite the Sankatnashan stotra / worship Ganesha before the campaign. Shiva propitiated Ganesha here, received the bija-mantra, and felled Tripurasura with a single arrow. The grateful Shiva consecrated/anointed the murti at this spot; the ancient name Manipur — after Shiva's pleasure — became 'Ranjan' (delighted) + 'gaon' = Ranjangaon.