From Sega Retro
Alex Kidd is a pint-sized, big eared hero who was the unofficial mascot of Sega prior to Sonic the Hedgehog's release in 1991 for the Sega Genesis. His games appeared on both Sega Master System and Sega Genesis/Sega Mega Drive consoles. He has starred in a total of six games before being phased out. Since then he has only made cameo appearances in various Sega games.
Alex Kidd is prince of planet Aries, son of King Thunder (sometimes romanized as 'Sander', in Enchanted Castle referred to as 'Thor'), and twin brother of Egle (sometimes translated as 'Igul'), the crown prince. Before the events of Alex Kidd in Miracle World, he has spent seven years living on Mount Eternal studying under his spiritual master St. Nurari, to master the Shellcore technique; an art that concentrates power in ones bare fists, making them capable of shattering rocks. On his way back home after his training had finished, he comes across a dying man who hands him a Sun Stone medallion, and tells him that King Thunder has gone missing. To make matters worse, an evil usurper named Janken the Great has kidnapped both Prince Egle and his fiancée Princess Lora, occupied the capital kingdom Radaxian, and dispatched numerous minions and henchmen around the entirety of Aries. Through the events of Alex Kidd in Miracle World, Alex Kidd manages to rescue Egle and Lora, defeat Janken, and find the Crown that can restore peace to Aries. His father however, remains missing. In his continued search, he gains word that King Thunder is alive and well on planet Paperock, so Alex sets out to find him in Alex Kidd and the Enchanted Castle. Traversing the dangerous lands, he gets challenged by several people for a game of Janken in order to let him on his way to the Enchanted Castle, where he eventually encounters Ashra for another Janken showdown. After Ashra's defeat, Alex reunites with his father and Ashra is revealed to actually be King Thunder's guard and servant; the king wasn't held prisoner at all, and was merely enjoying his time on Paperock. Having cleared up this misunderstanding, Alex sends word of King Thunder's wellbeing to Aries, and from then on the inhabitants of Aries and Paperock coexist in peace.