Okay, I did my best at translating it + providing the romanization. There might be errors, I didn't get it double checked with a native speaker.
Note: Title is a parody of 関ヶ原の戦い (Battle of Sekigahara), I think.
Koigahara no Kassen (恋ヶ原之合戦 Battle of Lovegahara)
Capitaro (かぴたろう)
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いざ進めよ 目指すは 君を待たせりし場所
iza susumeyo / mezasu wa / kimi o mataserishi basho
Now move / My goal / Is the place you are waiting
臆すな 臆せば 足は重くなる
okusu na / okuseba / ashi wa omoku naru
Don't hesitate / If I do / My feet will get heavy
この想いよ 君へと 導くしるべとなれ
kono omoi yo / kimi e to / michibiku shirube to nare
These feelings / For you / Become my friend that guide me
迷うな 迷えば 君は遠のくばかり
mayou na / mayoeba / kimi wa toonoku bakari
Don't lose my way / If I do / You will get further away
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可憐な姫よ 恋を知れば
karen-na hime yo / koi o shireba
Sweet princess / When I know your love
君が為に 強さを身に纏う
Kimi ga tame ni / tsuyosa o mi ni matou
I will be clad in strength / For you
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胸が打ち鳴らすその鼓動が 戦の始まりを告げる
mune ga uchi-narasu sono kodou ga / ikuka no hajimari o tsugeru
This beating that rings in my chest / signals the start of war
想い描いた僕の横顔 叶うその時を夢見て
omoi egaita boku no yokogao / kanau sono toki o yume-mite
The profile of my face that drew up feelings / Dream about the time they will be granted
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いざ射止めよ 狙うは 君の幸福のみ
iza itomeyo / narau wa / kimi no koufuku no mi
Now win it / My aim is / Only your happiness
惑うな 惑えば 想いは伝わらぬ
madou na / madoeba / omoi wa tsutawaranu
Don't have doubts / If I do / My feelings won't reach you
囲い国の 娘が 日々に挑んで散った
kakoi kuni no / hime ga / hibi ni idonde chitta
In a closed-in country / The princess was / sought after and scattered day after day
されども 言うのが 僕の決意は固し
saredomo / iu no ga / boku no ketsui wa katashi
Even so / What I'm saying is / My decision is firm
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一人女を 磨いてきた
hitori onna o / migaite-kita
one woman / refined
今日の為に 身の矢を武器に取れ
kyou no tame ni / mi no ya o buki ni tore
For today / I will use my body as an arrow for a weapon
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強く打ち放つ矢の切先で 君のその心撃とう
tsuyoku utchi-hanasu ya no kissaki de / kimi no sono kokoro utou
With the arrow tip that shoots off strongly / Let it hit your heart
君がそこに持つ恋ヶ原で 僕の命運は別れる
kimi ga soko ni matsu Koigahara de / boku no meiun wa wakareru
At Lovegahara where you are waiting / I separate from my fate
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苦き心 苦き思い 抱えし日は 長く続く
nigaki kokoro / nigaki omoi / kakaeshi hi wa / nagaku tsuduku
Pained heart / Painful feelings / The day I have you / continues to be far off
行けど行けど 君は遠い 道は長い
ikedo ikedo / kimi wa tooi / michi wa nagai
Go and go, but / You are far away / The road is long
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胸が打ち鳴らすその鼓動が 戦の始まりを告げる
mune ga uchi-narasu sono kodou ga / ikusa no hajimari o tsugeru
This beating that rings in my chest / signals the start of war
============================================
強く言い放つその言葉が 君のその心射貫こう
tsuyoku ii-hanatsu sono kotoba ga / kimi no sono kokoro inukou
These words that strongly declare are / Let me pierce your heart
二人出逢うこの恋ヶ原で 君との運命よ 繋がれ
futari deau kono Koigahara de / kimi to no unmei yo / tsunagare
At Lovegahara where we meet / My destiny with you / Ties us together