The people that are the strongest and/or have political power are in the student council or in the "Union". So the most important people of Musashi （main city/ship) are:
Union
President: Aoi Toori (MC, Human)
Vice-president: None (at the start)
First Member of the Special Duty (Intelligence): Tenzou Crossnight (Ninja)
Second Member of the Special Duty (Judgement): Kiyonari Urukiaga (Half-dragon)
Third member of the Special Duty (Actual Work): Margot Knight (Black witch)
Fourth Member of the Special Duty (Actual Work): Marga Naruze (White witch)
Fifth Member of the Special Duty (Actual Work): Neito Mitotsudaira (Knight)
Sixth Member of the Special Duty (Actual Work): Naomasa ("Mecha")
Student Council
President: Aoi Toori
Vice-president: Honda Masazumi (Negociations)
Treasurer: Shirojiro Bertoni (Money, money, money)
Treasurer assistent: Haidi Augesaraver (Shirojiro's partner)
Secretary: Neshimbara Toussan (Strategist)
There are a lot of other important characters
About the MC: He is a very fun character, is pervert, plays eroges, likes to be naked (even in some serious situations), is idiot, but has charisma and is the "king" of his class. Btw, his class is just like the top class of Musashi.