Let me transmit to you a theory... a theory that perhaps a great legend is true.
This is a jukugo word, which usually means on'yomi readings from the kanji. You just have to remember that 伝 is read as でん in this case. Just imagine yourself sitting in your den (でん) as you get cozy and listen to this theory about a great legend.
When you hear "a legendary Irish hero," who comes to mind?
Girls love you, man. You are legendary, seriously!
According to a legend, there is a fugu that eats tofu in this ocean.