Hotaru no Hikari (ホタルノヒカリ)

Someday surely I (topic) hand-into-do (it.is)

手にする ('to put in one's hand') is an idiom for 'to get / obtain'. Stronger than 持つ ('hold'); implies finally acquiring something one has been chasing.

Fleeting heart in, softly, light, burn-go (imperative)

儚き is the classical attributive form of 儚い ('fleeting, transient'), one of the most beloved literary words in Japanese — often paired with 命 (life), 夢 (dream), 桜 (cherry blossoms). 儚さ ('the quality of fleetingness') is a deep cultural value (mono no aware).

Chest's impulse, want-to-cry (stem)

衝動 ('impulse / urge') is a sudden internal pressure, almost involuntary. 衝 ('thrust / charge') + 動 ('move'). Common pairings: 衝動買い ('impulse buy'), 衝動的 ('impulsive').

Wound in-the-state, nodded (tag)

頷く (うなずく, 'to nod') vs 頭を振る (shake head). 頷く specifically means a small affirmative nod — common in Japanese conversation as a quiet 'yes' or 'I see'.

Sad to-the-extent, life was-flickering

揺らめく ('to waver, flicker') is what flames, candle-light, and heat haze do — reminiscent of the song's firefly imagery. Compare 揺れる (general 'sway / shake'); 揺らめく is specifically the soft, undulating kind.

Sha-la-la, someday surely, hand-into-do-(emphatic)

手にすんだ casually contracts 手にするんだ — the る elides into the next syllable. Common shortcut in spoken Japanese.

Beloved person, you also coming-into-view (question)

愛しき is the classical attributive of 愛しい ('beloved, dear'). Same 〜き pattern as 美しき, 強き. 愛しい is itself an emotional 'dear / beloved' rather than the more romantic 愛している ('I love').

Dazzling moon (subject) softly tomorrow (object) illuminate, strongly strongly

まばゆい ('dazzling, blinding') is a literary alternative to 眩しい. The poetic kanji 眩 ('to dazzle') with the 〜ゆい ending feels softer and more song-friendly.

Tire to-the-extent intensely become heart in

Almost-stray memories (subject), again gently are-lit

はぐれる ('to get separated from a group') — what kids do at festivals when their hand slips out of their parent's grip. Used metaphorically here for memories drifting away. 灯る ('be lit', intransitive) is for lamps and candles.

Absorbed in start-running if, can-touch feeling-had

夢中で is a fixed adverbial — 'absorbed in / passionately'. 〜気がする ('to have a feeling that') is the standard intuition phrase: that-clause + 気がする = 'I feel like X'.

Think as-is, hand (object) stretch-out (emphatic)

思うまま ('as one feels / following one's heart') uses 〜まま on a verb-dictionary. Companion phrase: 思うままに ('as I please / following my will'). Distinct from 思っているまま (state of being in thought).

Heart-tight to-the-extent, life baring

むき出す literally 'bare / strip exposed'. Used for fangs (牙をむき出す), for emotions (感情をむき出す 'wear feelings on the sleeve'). Aggressive — pure exposure with no protection.

Continuously sing-keep-going

Tremble chest in, softly, light, burn-go (imperative)

Beloved person, you to reach so-that

Verb-dictionary + ように expresses purpose ('so that...'). Distinct from ために which is for actions you control. ように is used when the outcome is hoped-for but uncertain: 届くように ('so that it reaches'), 上手になるように ('so that one gets good').

Endless sky in, softly, feelings let-pile-up, strongly strongly let-resonate

Causatives 積もらせる, 響かせる ('let X happen / make X happen') with て-form imperative force = 'let them happen, please'. Causative + て is the soft-imperative way to say 'allow / make X'.

Firefly (topic) burn-out (stem), scatter, vanish-go chest in

Verb stem + 尽きる ('exhaust completely'): 燃え尽きる ('burn out completely'), 力尽きる ('run out of strength'), 言い尽くす ('say all there is to say'). Adds total exhaustion to the base verb.

Softly, dream (vocative), shine

Vocative よ addressed to a dream — same poetic device as 鏡よ鏡 ('mirror, mirror'). Used for fairytale-like address to inanimate things or abstract concepts.

Beloved person you also don't-forget

Verb-negative + で is a soft prohibition: 忘れないで ('don't forget'), 行かないで ('don't go'). Less harsh than 〜な ('don't!'). Standard in songs and gentle requests.

Glitter summer in, softly, wish

きらめく ('to glitter, sparkle') is the sound-symbolism verb for tiny lights — stars, fireflies, dewdrops. Pairing with 夏 evokes the iconic Japanese summer images of fireflies and tanabata stars.