The Demon Spear Psynergy series is the Samurai class series' variant of the Support Psynergy series, Impact. It is similarly a Jupiter based Support Psynergy found throughout the Golden Sun series. For all practical purposes it is identical to the Impact Psynergy series.
Demon Spear is used to Boost one Adept's Attack by 25%, and can be used again to increase it to 50% (the maximum any stat can be raised above its standard value). This Psynergy costs 7 PP and is available at level 5.
Angel Spear is used to Boost the party's Attack by 12.5%. It can be used repeatedly to further increase the party's attack, up to 50% higher than its starting value. It is available at level 21 and costs 12 PP.
A fairly staple move within the RPG genre, raising your own attack can be a valuable tactic. However, most bosses can cast the Break Psynergy, and it only lasts for a short period of time, meaning that to make it useful, the increase in damage dealt before it wears off must exceed the damage that could be done through attacking normally. However, due to the attack multiplying effect, this becomes more valuable as the party progresses, both by buffing the party by a larger absolute value, and by increasing the base damage to be multiplied when using moves such as the aforementioned Call Dullahan Psynergy. This, along with the low PP cost, make this Psynergy series a highly practical one. When compared to the Impact series, the low PP and high base attack of the Samurai class means that it is probably more effective to have someone else (such as a Jupiter Adept) cast Impact on them, rather than the other way around, but this depends on the specific composition on the team.