A quesiton for Weeb Mari

"Mari can i ask you something?"
"Sure go ahead"
"What does oneesan mean? "
Mari shivers while her nose starts to bleed a little
"C-can you repeat that... slower
"uh"
"Oh-nee-san"
Mari squeals with delight and runs over to the bathroom
"OHMYGOD OHMYGOD OHMYGOD HE ACTUALLY SAID IT"
Mari is fanning her face
"OHMYGOD THAT WAS SO CUTE"
she gets some tissues to cover her nosebleed
"I HAVE TO GET HIM TO SAY IT AGAIN"
Mari grabs a tape recorder from the attic and comes over to Sunny
"Ok Sunny, can you say 'Onee-san' again?"
Sunny nods
"Oh-nee-san"
Mari's face starts to look flushed
"Say it normally, Sunny"
"O-Onee-san"
Mari's face becomes even more flushed
she runs over to the bedroom
"OHMYGOD I CANT BELIEVE I GOT THAT ON TAPE"
Mari audibly squeals
after that day, Mari asks for Sunny to call her 'Onee-san' at least once a day
One day, when Sunny calls her 'Onee-san'
She gets wet
Mari notices and then proceeds to the bedroom

A FEW DAYS LATER

Sunny has been wondering
what did 'onee-san' mean?
he asked that to Mari a few days ago, but she didnt give an answer that time
He asked Kel & Hero, both of them were stumped
So were Aubrey & Basil
this did little to dissuade Sunny
He went to Mari
"Mari, I asked you this a few days ago, but I never got an answer"
"What does Onee-san mean?"
A small dribbling of blood comes from Mari's nose
"O-Oh I forgot about that. Sorry, Sunny."
A-Anyways, Onee-san is Japanese for 'Big Sis'"
"Get it now, Sunny?"

Sunny nods his head
"But Mari, why don't I just call you big sis?
Mari grows a look of annoyance
"I just like it when you call me that, makes me feel more..."
"Loved."
"But Mari, I already love you."
Mari blushes a bit
Mari goes in to give Sunny a bear hug
You're so sweet, Otouto-Kun."
Sunny's ears perk up a bit
What's that mean, Onee-San?"