This is a great point to bring up! This is one instance where I think the romanization can be misleading...we romanize "ぎ" as "gi", but it's not exactly the same sound, it's more that this romanization was chosen because "g" is the closest match to the consonant, not that it's an exact match.
There is a broader range of sounds in Japanese that are perceived as "g" than in English. Some Japanese pronounce it closer to a hard "g" sound like in English (rarely as hard) but others pronounced it more like a "ng", a consonant that is not used to begin words in English, but is common as an initial consonant in Vietnamese and several other languages. The "ng" sound can sound very soft. There are also a range of subtle variations kind of intermediate between these two sounds. The way the sound is pronounced also depends on context, like the surrounding syllables, and the person's mood or speed of speech, so one person might pronounce syllables we romanize as "g" harder in some words or settings than others.
The way the computer voice pronounces this particular syllable, actually sounds pretty typical to me relative to how I have heard native speakers pronounce it.
In order to understand spoken Japanese, you will need to start perceiving all this range of sounds as corresponding to the sounds we romanize as "g". You will definintely hear numerous native speakers who pronounce it even more softly than in this recording, so this is something you need to address if you want to have good listening comprehension.
Speaking the other way, it's less of an issue because if you use a harder "g", Japanese people will usually understand you just fine...but being aware of this difference and softening this consonant can help you sound more natural or like you have less of a foreign accent.
If you have a Mac, go to System Preferences > Dictation & Speech > System Voice > Customize... > then choose a Japanese voice and just highlight the text you want to hear pronounced, right click it, go down to Speech > Start Speaking and voila, instant pronunciation guide. (Though from the looks of it, Japanese isn't all too hard to pronounce, but whatever.) You can obviously do this with whatever language you want if Apple has the TTS for it.
Because here the う doubles the お sound in こ. In romaji this would be written koo or ko̅. Another common example is To̅kyo̅ とうきょう. い has the same function for え ending syllables.
I doubt it. Ginko, or ギンコ, is a name of Mushi-shi’s protagonist. Ginkō, or 銀行 (ぎんこう) means bank. As you can probably tell, the word for bank has an accent bar which differentiates the pronunciation between the two.
Of course, Ginko’s name could be a reference towards bank, but I’d doubt it. I’m not caught up in the manga though, so maybe it could be valid.
Yes, that's correct. Those "two lines" are galled dakuten (though more commonly called tenten), and they "soften" the consonant element of a character by adding voicing to otherwise unvoiced consonants. They can be applied to the ‹K›, ‹S›, ‹T›, and ‹H› series of characters, but not to any of the others.
かきくけこ → がぎぐげご = ka ki ku ke ko → ga gi gu ge go
さしすせそ → ざじずぜぞ = sa shi su se so → za ji zu ze zo
たちつてと → だぢづでど = ta chi tsu te to → da ji zu de do
はひふへほ → ばびぶべぼ = ha hi fu he ho → ba bi bu be bo
There is also another diacritic that takes the form of a small circle in the top right. It's called handakuten (though more commonly called maru). Handakuten can only be applied onto the ‹H› series and makes them pronounced with a ‹P› sound instead of an ‹H› sound.
はひふへほ → ばびぶべぼ → ぱぴぷぺぽ = ha hi fu he ho → ba bi bu be bo → pa pi pu pe po
Yes it actually is pronounced "ginkoo" or more accurately "ginkou" instead of just "ginko". As I said elsewhere in this discussion, it's a good idea to go to Google and search "Japanese long vowels" (and while you're at it, look up "Japanese double consonants" too) before you go any further. Unlike English, which is a syllable-stressed language, Japanese is rhythm-timed; it doesn't have stressed syllables (at least not in the same way as English) instead you tell similar sounding words apart by the verbalized length of their vowels and consonants.