Take a look at this map.
IIRC, the Empire of Nicaea was the direct successor state to the destroyed Byzantine Empire post-4th Crusade which IOTL went on to reconquer it's lost territories via war with the Latin Empire some decades later.
But what if, instead of taking on the Latin Empire, the emperor (Michael VIII) strikes east at the Turks first? Could he crush the Sultanate and if so what would be the effects?
Plausible reasoning could range from wishing to gain a more defensible foothold in Anatolia before attacking Constantinople to taking the loss of the capital as an opportunity to breifly shift focus to taking back Asia Minor.