By solo... you mean only one character for entire game (exluding generations changes)? While I didn't play almost at all... no. Big no
. :D It's impossible... I think even with, assuming there is something like that, NG+ and putting everything in the character, I would say it wouldn't be possible. Game is based on using the formation-focus attack. Also - lack of specific 'jobs', so to say, would also be a disaster.
Well, I just had 4 deaths in a single normal non-boss fight with full party. So perhaps you might be right.
Though I am thinking to try solo challenge myself on Hard mode of Agarest 1 to see how far I can go. I will invest only in VIT and a bit in MAG (to raise RST), and use all DEF/RST gems. And then rely on EX-Skills to kill anything, because ATK and HIT will be very low...
In case with Agarest 1, it looks to be double solo challenge, 1st part - before 2nd Gen., and 2nd part - before you get first Forbidden Tome to make marionettes. So I think to try 1st part with Leo, 2nd part with Zerva, and then with Leo again.
...but I am a bit afraid of all the grinding and I hope someone else will try this challenge :P