Hello,
Despite my attitude to ads on SPP, I have decided to post my XY&Z and SM investigation.
I think all of you know how Satoshi's memory works. Something in front of his eyes may remind him of something else related. We usually see it as flashbacks or his words like it was with a Pochama in XY 024. Let me enumerate things that could definitely remind Satoshi of Hikari as well as a sign that he romantically loved Hikari in BW2 and didn't romantically love Serena in XY&Z. I will also tell who can be Hikari's formidable rival in love.
1. You obviously know Hikari's catchphrase "daijōbu, daijōbu".
Ironically, in DP 191 when she says it again, Satoshi answers, "You always say "fine" when it's not fine". I wish he got thunderbolted by Pikachu every time Hikari's catchphrase was used by him.
He did it at least 3 times in XY&Z and at least 3 times in SM, not to mention that its context often looked similar to that of Satoshi's answer from the past (before getting a cold in XY, being unprepared for presentation and hitting the hurdle during springboard competition in SM).
Actually, Satoshi regularly using it is a serious prove that of all the girls Hikari had the greatest impact on him.
2. Species of once owned Hikari's Pokémon or carried by her.
In XY&Z (including movies) Satoshi saw Pochama, Pachirisu, Mimirol, Manmoo, Buoysel. If he remembered Pochama, he remembered everyone else from Hikari's party. Furthermore, in SM Satoshi saw a Shaymin which could remind him of his adventure with Hikari and Shaymin from the film "Giratina and the Sky Warrior".
3. Legendary Pokémon - Dialga, Palkia and Arceus.
It also has a prove because Satoshi mentioned meeting Arceus before in the movie "Archdjinni of Rings: Hoopa". Also seeing Dialga and Palkia could remind him the adventures with Hikari in Alamos and Michina towns.
4. Citron - Eureka quarrels.
The episode XY 045 focuses on Citron and Eureka having quarrels and then making up. Even Satoshi said in thoughts something like: if two people fight, they care deeply for one another. I wonder if he thought of Hikari at that time...
5. A high-five with Mao in SM 026.
Satoshi (almost) never did his and Hikari's trademark gesture without her. I am sure Hikari immediately popped up on his mind. I wish Pikachu added a massive thunderbolt here too, for precaution.
6. Playing Pokémon ping-pong with Mao in SM 066.
Satoshi (almost) never did this after he experienced it with Hikari in DP 124. I think he could also remember that time.
As you see, Satoshi doesn't seem to have a chance to forget Hikari.
Now about Satoshi, Hikari and Serena.
Usually, the dearest missable people are seen off with a sad and/or serious face
and those, whose absense is easy-going, are seen off with a smile.
Let us compare:
DP 191 - Hikari seeing off Satoshi -
, on the verge of crying.
BW2 009 - Satoshi seeing off Hikari -
(this emotion is seen immediately after he turns around from the leaving plane)
XYZ 047 - Satoshi seeing off Serena - no
, smiling.
Only Satoshi and Hikari seem to have the relationship of two people dearest to each other. And there was no Takeshi in BW2 009, so Satoshi's sad and serious emotion was only due to Hikari leaving Unova. If Satoshi loved Serena, he would be sad and serious, besides, if the kiss was really on his lips, he would hide his eyes under his hat.
And lastly, the girl, who could be in competition with Hikari for Satoshi's love, is Mao. Throughout all the SM saga they spend much time together, have something that looks like dates (SM 004, SM 018, SM 035), are often seen physically close to each other, sometimes have similar reactions, sometimes have arguments. Not to mention Mao's cat-like face fetish, when Satoshi was in female nurse Joy clothes, Satoshi loving her food and his Mokuroh often wanting to approach her Amakaji and its evolved forms.
Thank you for reading.