Katsuragi Musashi, Called "Unsinkable" by some due to the rumor that he has never lost a fight even though it appears that this is merely due to lucky coincidences in his otherwise very unlucky life. This nickname, he believes is somewhat fitting because before the series a ship he was on sinks killing everyone onboard including his parents except for him so now he lives alone.
He is childhood friends with Akane who often comes over to his house, offering to cook for him or care for him. Also living at his home is the mysterious Kagura who along with saying he would be the next student council president and she would give him herself as a "reward" also often gets katsuragi in tons of trouble when Akane comes in on easily misunderstood situations. Apart from these two lady friends he also is friends with Kaoru and Nagare whom he cares for greatly and goes out of his way to protect should the situation call for it.
As far is his relevance plot wise is concerned, he is the Main Male Protagonist who is said to be the next student council president who will protect the school by Kagura Mami although it looks the rest of the student council isn't so sure. Also by opening the "un-openable door", wolf DNA inside of him has awoken giving him special powers, which explains the tail he has to sport at school.