I felt like I really had to clear this up for people who've played SMT II.

If you haven't played SMT I in the SNES RGR, you should play it because since SMT II in the GBA RGR is Japanese, you will not know what the choices are when you pick Talk in battle and what Steven says when you find him.
I also had clear up the Alignments that all demons have.
L-L = Light, Law
L-N = Light, Neutral
L-C = Light, Chaos
N-L = Neutral, Law
N-N = Neutral, Neutral
N-C = Neutral, Chaos
D-L = Dark, Law
D-N = Dark, Neutral
D-C = Dark, Chaos
*Note: All Dark demons, regardless of your level and alignment, are not recruitable.
They must be made from fusions.*
Also, three special types of demons can be made. For the first, a perfect example is Kerberos, the temporary demon you get from the mansion in the woods. Demons like these are demons that will bypass the level cap and join your party, regardless of alignment.
For the second are bosses that can only be made after you beat them. One example is Beelzebub. As for the last, you can fuse demons with certain weapons in this game, but you need a special item for it. The item is called Renki-no-ken, but in the game, it is pronounced Renki 非理解.