蜃気楼 means “mirage,” a rare and poetic word for an image that appears in the distance but disappears when you try to reach it.
In the song, the singer compares someone who has vanished to a mirage, giving the disappearance an elusive, dreamlike feeling. It is a memorable word because it captures both beauty and impermanence in a single image.
Sakanaction turn a rainy night into a dance floor here. The song opens with the singer jumping like a primary school kid, skipping over puddles after the rain like a stone skimming across water. Then the girl he's with joins in, hopping over a puddle like a water strider (an amenbo, the little insect that skates on the surface of ponds). It's playful and a bit silly, and I love that.
But there's a catch hiding in the katakana lines. Phrases like ヨルニニゲタダケ (I just ran away into the night) are written in katakana instead of normal kanji and hiragana, which makes them look stiff and robotic, like a mantra. He pretends he saw, pretends he forgot, pretends he heard, and walks straight past tomorrow and past the morning. Then she vanishes like a mirage, and even the sound of the sudden shower goes quiet, as if saying goodbye.
The second half flips the mood. The repeated 今泣いて (cry now) lines say: cry now, and in a few minutes, or a few years, you'll move on. By the end he's imagining himself heading somewhere far away, toward where he wants to go, and the last line asks 笑っていたいだろう (you want to keep smiling, right?). It's escape turning into hope.
Learner tip: watch the pattern 〜みたいに (like a...). It shows up again and again here, and it's one of the most useful ways to compare things in casual Japanese.
Sakanaction formed in Sapporo, Hokkaido, in 2005, led by singer and guitarist Ichiro Yamaguchi. The five-piece mixes alternative rock with electronic, pop and new wave, and is known for songs like "Aruku Around" and "Shin Takarajima".