Sheet processing apparatus and image forming system incorporating the same

A sheet processing apparatus comprising:

• a roller pair configured to convey at least one sheet;
• a first sheet conveyer configured to convey the at least one sheet to the roller pair;
• a second sheet conveyer configured to convey a following sheet subsequent to the at least one sheet;
• and
• circuitry configured to
• cause the first sheet conveyer to butt a leading edge of the at least one sheet to the roller pair,
• cause the roller pair to rotate in reverse to align the leading edge of the at least one sheet in response to the leading edge of the at least one sheet butting against the roller pair, and
• cause the second sheet conveyer to convey the following sheet such that a leading edge of the following sheet butts the roller pair aligning the leading edge of the following sheet and the leading edge of the at least one sheet.