[Can someone tell me about Suika2 engine in detail?]

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eg: buttons for the menu option. I understand that first two values located the center and next two values allocated the size for them but when I actually tried to implement it in that way, it isn't working very well.

Sorry, I realized that the command reference is incomplete.

@menu menu.png menu-selected.png START 640 480 240 120

"640 480" locates the top-left position of the button on the screen.  It's not center position, and it's not documented.  I'll add some explanations to the command reference. Thank you for pointing out.

In this way, your feedback is important for this engine.  So please feel free to contact me with any comments or questions.

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It would certainly be very nice if there was a video tutorial for it

Okay, I'll put it on my TODO list's top.  Since this is my first time to edit videos, it will take several weeks.

[Can someone tell me about Suika2 engine in detail?]

Hi, actually I am the developer of Suika2 you're talking about.  Unfortunately, your e-mail didn't reach me.  If you have any questions, I would love to answer here on this board (or resend me an e-mail.)

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But I don't know if it can be used for making a full VN

Suika2 is a fully featured VN engine except movie playback.

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other than the github link for its documentation there's nothing about it to be found on the net

Yes, it's not that famous.  But at least, there is a semi-commercial full VN that uses Suika2.  Search for "灰翼のロードピス" if interested.  (ATTENTION!!! X-RATED!!!)

A good side of few users is that I can take a lot of time to support every single VN developers.  Feel free to contact me.  I'll introduce new features for you.