>>712555586
Introducing and front-loading characters can help but anticipation and further story relevance than the occasion they were introduced in can also help.
Sakurako showed up in the story but wasn't released until the rerun of Hinata/Ui's event which was after Volume F reminded people she existed. Despite getting her regular version and idol alt released, she hasn't necessarily been given a "focus" event since the idol event was primarily about Mari.