You’ve conveniently latched onto just one of the things I mentioned. I brought up the kiss scene and the park scene, where the romantic aspect is explored much more deeply.
If you genuinely think Luna doesn't have romantic feelings for Nao, I don't think we're reading the same story.
Chapter 11 page 16.
Luna initiates a kiss, it's a fairly short and standard one on the lips, no tongue. Ends with a proud smug look after a job well done. As if she was kissing a young child. Contrast when Naoto, who
does have romantic feelings for Luna initiates the kiss immediately after page 16. An adult one, the type that made her want it to never end, Luna had to cool down in the showers.
Chapter 19.2 page 19.
Park, Naoto initiates the embrace, Luna drowns in it. Naoto noticed her emphasis on "Nao-kun" as if it was a shadow of someone else.
She still sees her "younger brother Nao-kun". <- ATTENTION! You'd think the ghost of Nao-kun past would have left by now, but nope, he's still there in Luna's diamond-shaped eye lens.
You want more?
Chapter 8 page 34~36
After Naoto "marks" his treasure (read: Luna) by giving her a hickey, she initially thought "Nao-kun was just homesick". When the realization of what just happened kicks in and she starts to heat up, she just thinks she only caught Naoto's fever(illness).
Chapter 9 page 21~22.
Naoto confesses to the drunk Luna that he wants them to be close again like they used to. Luna claims their feeling is mutual. Luna immediately asks Naoto to play their childhood games. Luna reverts back to "Big Sis Luna and Younger Bro Nao-kun", until Naoto snaps her back to the present.
Chapter 12 page 24
Luna tells Nao-kun she loves him. This is with the "lighter" "suki" and not the "romantic" "aishiteru".
Chapter 13 page 15
Hiba asks Luna if she's worried that Kawashina would steal away Nao-kun. Luna claims that Nao-kun wasn't Luna's to begin with.
Chapter 15.2 page 8
Turning point, this is where she gets conscious of Nao-kun as a grown man.
Chapter 16.1 page 10
Naoto explains to Luna when he said "he likes her", Luna says she feels the same way, that she treasures him like a real younger brother.
Chapter 16.1 page 12
Luna was pretending to sleep, but she hopes that "things will work out this time", and that "the Nao-kun now" would be able to accept "Luna". This means "Luna" did something with "flashback!Nao-kun" but the young Nao-kun back then wasn't able to accept "Luna". Gee, wonder if this has something to do with her no longer showing up to the countryside, with Naoto's mother withholding the reason why, 10 years ago... <- ATTENTION! This is important detail to remember as more of Luna's secrets gets revealed.
You’ve conveniently latched onto the idea that I completely deny any budding romantic feelings Luna would have towards Naoto. Maybe you just needed a quick reminder of the timeline.
Luna Pre-Middle School (Suffers from parental abandonment, is lonely and depressed in her own house)
-> Luna Middle School (Spends a few Summers with a relative[Naoto], considers it up to the present to be the HAPPIEST DAYS OF HER LIFE, cries at the thought of Naoto leaving her)
-> Luna 10 years prior to start of story (a still unspecified incident occurred that separated her away from Naoto, Naoto's mother refuses to give details, is part of Luna's 10 secrets)
-> Start of story (Reunites with Naoto, treats him the same as where they left off 10 years ago)
-> Chapters 1~11 (Naoto slowly working his way out of lil bro zone, Naoto is filled with determination to go all in for Alabama with Luna)
-> Chapter 12~15 (Luna slowly starts seeing the Naoto's growth as a man)
-> Chapter 16~23 (Luna hopes that "The Nao-kun of Today" can achieve what "The Nao-kun of Yesteryears" failed to do... which is to accept "Luna")
-> Chapter 24 (Luna realizes that "Luna" is taking initiative, but is afraid that doing so would cause "Nao-kun" to leave her once again)
-> Chapter 25
(Remember when I agreed with you that this is a stupid development? "Luna" backpedals and decides to erase her desires to become Nao-kun's "Luna-Nee" once again, unaware that Naoto WILL ACCEPT EVEN "LUNA", Luna isn't thinking rationally with her actions, she is recklessly going by emotions)