訴因 is read as そいん (soin) and means charge.
そいん
soin
うったえ
lawsuit
そしょう
litigation
うったえる
to complain
そじょう
petition
そつい
impeachment
そにん
a suitor
そついいいんかい
indictment committee
そきゅうりょく
appeal (e.g. of an advertisement)
うったえでる
to lodge a complaint
そがい
party not named in (this) court case
そけん
right to take legal action
そきゅう
appeal (to customers)