I tried doing my best even though I don't know any japanese. But the other translations were so bad it was unfappable. At least I hope this one is good enough.

Why don't you first try your best at learning Japanese...?

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the other translations at enlgihs is so bad that i decided ot trnalsate this job by me on english hope u enjoy
btw cant speak japanese nor english lol
please dot out if you find mistakes

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how do you know yours is better if you don't know Japanese?
coomer brain logic

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Well, at least your editing and typesetting is better than the other. I appreciate it.

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I can't speak to the quality of the translation itself, my skills are nowhere near good enough to judge that, but you have left a few things untranslated on various pages and your grammar needs some work.

Page 5 "I decided to help one of those fiend." "Fiends" is what you're looking for here. She's one of a group, the group should be plural.
Page 6 "I'm just an hostage". An is used before vowel sounds, a is used before consonant sounds. The H is not silent, so it should be "a hostage".
Page 7 "I could not leave her in this dangerous position". He's already taken her in away from her problem so it should be "that dangerous position".
Page 8 "I have almost come out of magic". You don't "come out" of anything when depleted, you "run out".
Page 9 "A type of demon that feed on men magic power". "Men's" is the word you need, as the statement is one of possession.
Page 9 "Clearly she have less magic power". It shouldn't be have in this case but "has".
Page 11 "I always ask permission before receiving a human magic power". Like the first page 9 issue, you've not indicated possession. "Human's" is needed here.
Page 19 "Semen full of the hero magic power". Once again, it needs to be possessive. "Hero's"
Page 26 "I want to do it with here chest". Looks to just be a typo, it should be "her".
Page 27 "Those huge, round breasts of her". Possessives do not seem to be your strong point, "hers".
Page 28 "Your penis want to do it". "Wants" is the word you're looking for here.
Page 32 "It feels so good that I can think about anything but her amazing boobs". He "can't" think about anything else.
Page 34 "Let's make a quick break". You "take" a break, not make one.
Page 35 "Take the time to catch your breathe". Breathe is an action, "breath" is what you'd catch in this case.
Page 35 "If she jerk me off". "Jerks" is what it should be in this case, not jerk.
Page 40 "How was did you find my boobs?". This could go two ways "How did you find my boobs?" or "How were my boobs?", but as written right now it's nonsensical.
Page 44 "How dou you like it?". The word is "do".
Page 50 "Her magic sucking power made me faint of pleasure". He fainted "from" pleasure not of it.

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... I am honestly surprised it didn't end up with the succubi sucking him to death and becoming the new demon lord.

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Definitely would be nice to get a translation from someone else who knows Japanese and English.

Reading through it it's not the worst I've seen but English mistakes like P6 "I'm just AN hostage" like LRaglan pointed out and:

P15: "Please. Leave it to me.... Feels good... I'll make it squeak" which was so nonsensical and bad I had to look up the RAW to see how you got it so wrong.

It's "Hora, watashi ni makasete kudasai.... kimochi yoku...Pyu pyu tte sasechaimasu kara ne" = "Here, leave it to me.... I'll make you spurt it out... and it will feel really good"

And I'm just getting started reading it. Anyway, really good doujin, would hope for a better translation.

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