Did he cause any of his family members to torment Uichi? No.
Let's get down to brass tacks. If the mom and sister were calm, supportive and reliable , good family members like him, then Uichi wouldn't have any stress at home.
And yet we're supposed to believe that HE's the real bad guy and the one to blame, not the mom for emotionally abusing Uichi and deliberately self-harming in front of him, or the sister for screaming at Uichi ?
How about the others have a little accountability for being such a bad mom and a bad sister?
You cannot be serious, if you are you're insane.
The dad is simply putting up a front of a "good father" by doing things by the definition of what a "good father" does but does not apply to the situation at hand.
Like when he gave the snacks to uichi, in his mind a "good father" would bring up snacks when a guest is over, but he sorely focused on the action of bringing snacks up it did not occur to him what kind of snack and he gave his son something that could literally kill him because of allergies.
He does not care about uichi, what he cares about is his mental image of what a "good father" is.
All of the family members are to blame, but the mom and sister only got worse because of the dads actions.
He enabled the sister by giving her money whenever she wanted and letting her do whatever she wants with no consequence. A good father would have disciplined her and punished her for what she's doing.
The mom was literally crying for help and cutting herself and he simply goes "Sounds rough, try harder!" with a smile on his face.
Hes delusional and so are you if you think he did nothing wrong.