Eternal Dark Knight, do you mean the Two Hands ability? I find the increased attack power is not worth loosing the option to equip a shield. If you meant Two Swords, that's a Ninja skill.

Earlier on, I found Koutetsu (moderate damage) and Murasame (heals HP) particularly useful Draw Out skills. Later on Kiyomori (Shell, Protect) and Kikuichimoji (straight line attack) pay for themselves in battle. Mamasune is a great Draw Out skill, but hampered by the fact you only have one katana, and if it breaks, you can't get a new one.