I spend the entirety of CTMEOY asking myself that. The best I can do is steal the translated lyrics from the OP and hope it makese sense.
(You know, I just realized, Hata wrote the lyrics to this song. I'd completely forgotten him mentioning it before Season 3 came out.)
Spoiler:
そこで笑ってて くれないか？
soko de warattete kurenai ka
Could you please keep on smiling?
小さい頃 星の数ほど夢を見て
chiisai koro hoshi no kazu hodo yume wo mite
In my childhood, I saw a countless amount of dreams like stars in the sky.
私が望めば なんでも手に入ると思ってた
watashi ga nozomeba nandemo te ni hairu to omotteta
I imagined that I could get anything if I wished for it.
でも欲しいものは 全部高いところにあって
demo hoshii mono wa zenbu takai tokoro ni atte
However, everything I wanted lay in high places.
背伸びをしても届かないから 見上げるのをやめた
senobi wo shitemo todokanai kara miageru no wo yameta
Even if I stretched out, I couldn’t reach them, so I stopped looking up.
だけどあの日 君に出逢った
dakedo ano hi kimi ni deatta
But then, I met you on that day.
微笑みをくれた
hohoemi wo kureta
You gave me a smile,
生まれきたその意味 知ったんだ
umare kita sono imi shittanda
And taught me the reason why I was born.
あなたがこの世界にいると
anata ga kono sekai ni iru to
Just believing that you’re in this world,
思うだけで生きていける
omou dakede ikite ikeru
gives me the strength to live on.
伸ばしたその手つかむよ
nobashita sono te tsukamu yo
I will grab your extended hand,
何度くじけたって構わない
nando kujiketatte kamawanai
no matter how many times I fall.
乗り越えるよ だから
norikoeru yo dakara
In the end, I will overcome it,
そこで笑ってて くれないか？
soko de warattete kurenai ka
so could you please keep on smiling?
(Yeah, still no clue on the apple thing.)