Is there hope for forgiveness for the one who committed suicide, but was a praying, believing person who never harmed anyone?

If the suicide was committed by someone in full possession of their mental faculties, then they have committed a grave sin and a major transgression, considered among the greatest of major sins. However, this does not render them an unbeliever according to the أهل السنة (Ahl al-Sunnah), and there is no objection to seeking forgiveness and mercy for them. Their fate rests with Allah's will; He may punish them if He wills, or forgive them if He wills. There is hope for their forgiveness, especially if they used to perform righteous deeds.