not going to lie, i was thinking first of ultimecia, and to try and keep it in family friendly terms, she can make one quite thirsty.
but you said to take this seriously. and since you set the limit of original appearance, that reduces the effectiveness of each villain.
panda picked exdeath, who is the only character in dissidia who can block all attacks, even chaos and feral chaos's attacks. jecht can block all but one of his attacks as well as all other characters too.
i mainly went with demonstrated power levels. that would make the pool of viable characters go down to just 3. ultimecia, kuja and jecht.