Cu Chulainn on the other hand, was a mighty warrior. He feel in love with Emer, but Fogall(a mighty chieftan) refused to allow her to marry him until he was a truly great warrior, so Cu Chulainn went to train with Scathach. There, he obtained his spear Gae Bolg, the Disembowler. He slept with her daughter Uathach, and also defeated Scatach's sister, Aoifa, and also slept with her. Then, near the end of his training, he slept with Scatach(you may be spotting a pattern here). After all this he returned to Fogall, and despite facing Fogall's greatest heros, he triumphed, claiming Emer as his wife. Fogall meanwhile jumped to his death.
The reason Cu Chulainn is Tower Arcana is because he was destined to be one of the greatest warriors of Ireland, but die young, which in every variant of his myth, he does. Usually, it's by forcing him into a spot where he must break an oath. Cu Chulainn had two famous oaths, to never refuse a meal and to never eat the flesh of a dog(he himself being the Hound Of Ulster). So his foes offer him a meal of dog flesh. Breaking one of those oaths weakens him greatly, and he is killed in battle. However usually, with his last strength he props himself up by tying himself to a rock so the enemy still thinks he is alive, until the goddess Morrigan, as a crow, sat upon his shoulder, showing he was dead.