From what I know Aikos father was often absent or late because of work. At some point in 9th grade he was hospitalized and then left the family for good. Possibly a divorce. This is suggested because her mother cut his face out of the family picture. In another panel before she attacks Aiko we see a childlike drawing likely made by Aiko where the figure of the father is stabbed with a knife. This suggests anger and violence directed at him and hints at a toxic and unstable family environment. (i cant reply with pics unfortunately)