The Quintessential Quintuplets: You can't address your parents chichi/haha, but can you refer to your parents as oyaji/otou-san/okaa-san?

Question

According to Yuta (whom I heard is apparently not well regarded in the subreddit r/learnjapanese but eh) in How Anya Speaks Japanese (Spy x Family): You can't address your parents as chichi/haha. Rather, chichi/haha is what you use when you refer to your parents to someone else...

Question 1: Oh wait. Yuta says someone else who is not your family member...so should you/can you/should you not use chichi/haha when talking to full (biological or adoptive) siblings? Half-siblings? Step-siblings (via marriage not adoption)? Cousins?

However I noticed in S02E12 of the anime adaptation of the manga The Quintessential Quintuplets:

The male protagonist Fuutarou says something like 'ore mo/no oyaji' (me and also my dad? or just my dad?) which is translated to 'My dad and I loved it' (The 'it' here is some kind of bread).

Not sure if relevant, but Fuutarou is addressing a non-relative, specifically (S02E12 spoilers)

Fuutarou's friend/classmate/tutee Miku Nakano. They're on an unofficial date. The bread aforementioned is related to the bread in the preceding link.

Question 2: You can't address your parents chichi/haha, but can you refer to your parents as oyaji/otou-san/okaa-san?

• Note: If the spoiler part is relevant, then please explain why.

Question 3: Btw, what's the female/matriarch/mother version of oyaji please?

Question 4: Actually wait I just remembered. There's this scene in S02E02 where 2 quints refer to their dead mom alternatively as 'okaa-san' and then 'haha'. Are they indeed both correct?

The identical quintuplets Nino (older) and Itsuki (younger and actually youngest; also the female protagonist) are arguing. Itsuki says 'Mother would be so sad if she saw us now.' (But since Itsuki says okaa-san instead of okaa-sama, I guess 'mom' is a better translation?) Nino replies 'Let her go already. And quit trying to act like her replacement all the time.'

Some notes: (Also some S02E06 spoilers.)

1. The characters in this scene are the 5 quints and their tutor/friend/classmate Fuutarou (the male protagonist).

2. It's actually revealed in S02E06 that Itsuki was the most impacted by their mom's death and continues to be more impacted than the other quints.

Answer 1

Q1：No, chichi/haha won't be used when talking to siblings, generally speaking. The basic rule is that honorifics are not used when talking about people "inside" to people "outside". In this case, inside/outside border is whether or not one is a family member. So, assuming the case of talking to siblings in an ordinary family, all are "inside"; as such the rule does not apply and otou-san/oka-san (or whatever is used for calling father/mother by the speaker) are used when talking about father/mother to siblings. For comparison, if talking about father/mother to your teacher, say, you will refer to father/mother by chichi/haha.

Q2 : Yes, oyaji/otou-san/okaa-san can be used in theory. But whether "oyaji" sounds natural depends on many factors, e.g., the age of the speaker.

Q3 : It is ofukuro.

Q4 : I briefly checked the anime. The second part uses 'hahaoya', not haha, and is talking about generic 'mother', not about their particular mother. So it is not directly relevant to the current question.

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Re Q1. Another example. Suppose you have a colleague named Tanaka. Normally you talk to him as Tanaka-san. But when talking to a third person from another company, you refer to him as Tanaka because Tanaka is 'inside' and the third person is 'outside'.

Answer 2

You can refer to your parents as chichi and haha. They probably most closely translate to "daddy" and "mommy", so you can get some feeling on how this would make people think about your relationship with your parents if they overheard this.

So, compare "Mother, can I have money [e.g. for my education]?"

"Mommy, can I have money [e.g. for toys]?"

Someone could even say that "mommy" would be disrespectful to your parents after a certain age, but that would need debated.