松葉: pine needle

being on all fours

four leaves, namely, those of the four-leaf clover

四葉: a female given name

the occasion of summer

一番: number one, most, -est

一番: number one

to go; to come to one's place / to (a letter) be delivered / to depart / to rely (on a method) / (年が～) to age / (うまく～) to go well / イく: (slang) to have an orgasm, to come, to cum

past tense and perfective aspect of 行く (iku) [godan]

past tense and perfective aspect of 行う (okonau) [godan]