Mithos is a Half Elf Angel being of the world of both Sylvarant and Tethe'alla, Mithos plan is to create the World Regeneration journey to allow a child of angel being to unlock the four seals of a world and going to the tower of salvation only to become the vessel of Mitho's sister Martel, Mitho's is seriously a bad dude when you get past is boyish form hes really trying to destroy both worlds only to revive his sister, Mithos goes crazy with his ideals that the two other Angels or Seraphim that helped him bring an end to the great war Yuan and Kratos both betray him for what he is planning to do Martel as well was in sorrow when her conciousness was brought through with help of Colettes body as a vessel, Martel tells Mitho's that what he has been doing is wrong, Mitho's would try to bring back his sister and make a new age called the "Age of Lifeless Beings". Mithos also puts on another form in which people call him Yggdrasil something that you might have heard from
Tales of Phantasia
Mithos when in his Yggdrasil form is probably the third hardest boss battle in the game probably, his attacks can range from upclose attacks to Area-of-effect attacks to distorting attacks which can really set the party apart and alot of managing of everyones health might have to be taken care of and his most dangerous attack is probably is Judgement abillity which just rains down beams of light that can do about 1k damage to a party member, Now when in his Mithos form it can be a good 15 minute battle if perpared (and if you dont cheat) Mitho's can heavily damage the field and scatter members by using a scatter attack, Holy Lance, Judgement and others, since he is a light bassed character light attacks are NOT good at him what so ever so make sure to have some black quartz with you, Mitho's most powerful attack once again is his Judgement or this area effect attack which basically puts different types of diseases or paralizing motions on all party members having you to use Raine to use her purify technique or massive amounts of items to get all the effects off.
Mithos....dosent exactly have any relationships with any characters when it comes to like freindship or love, the only type of relationship he has is a bond with his sister that keeps him going through all the times he tries to destroy the world.