勢威 is read as せいい (seii) and means force.
せいい
seii
いせい
power
いせいよく
with energy
いせいがいい
vigorous
いせいのいい
high-spirited
せいりょくけん
sphere of influence
せいりょくかくだい
expansion of one's sphere of influence
せいりょくけんない
within the sphere of influence (of)
いきおいをふるう
to wield power
せいりょくはんい
せいりょくきんこう
balance of power
せいりょくはくちゅう
(the two sides) being evenly-matched in influence or power
けんい
(an) authority (on)