Ch0: It was heavy rain as if mourning the day tomorrow that will not happen. -> It was heavy rain, as if mourning the following day, which may not happen. Using day and tomorrow, if you read it out loud, it sounds harsh, also commas missing. 

A sad scene that somehow calmED the heart of a lost person in this dark place. Attention to keep the same verb tense through the entire narration. No need for comma if you use that in this one. lost person not person lost, both are grammatically right, but this way it sounds a lot better. Readability is the standard for readers to stick around. 

 Ch1:A girl was sitting on a public seating basking under the magnificent golden rays of the sun while enjoying the solar light.

The girl wore a normal patient cloth, pants, a shirt, and some slippers. (Girl first sentence, then again on this second one.) Why not just:A beautiful figure remained seated in a public bench, basked under the magnificent golden rays of the lustrous sun. Its solar light, permeated her white patient cloths (no need to put pants+shirt), and some slippers. Above her waistline (if long hair) Above her chest (shorter one), dark-silver colored hair dimmed the light intensity, as the contrast was, but one of many features that by her own standards, made her believe herself to be, 'the most beautiful girl out there.'

she had dark-silver colored hair, and was by her standards "the most beautiful girl out there". (Lack of capitalization, the full stop stays inside the quotation marks, and usually when referring to so an idea, you use 'the most...' Double is dialogue only. Oh, yeah. I forgot to say, but just to clarify, I am no Vampire, I am just your "average human being ?", I guess? (You don't need quotation marks here, since you're telling us as the narrator.)

"hmm, Alice nee-Chan, are you dying again? you are not moving, and your face is pale again, with an emotionless look. Are you breathing ?"  Capitalization again, extra space at the end. With an emotionless look, sounds like what the character is seeing, not something she'd tell.

"Hmm, Alice nee-Chan, are you dying again? You haven't moved for a while now..." The emotionless look on the girl's expression worried the friend<character name> "Your face is pale again... are you sick?" <he placed his hand near alice's nose to check if she was breathing.

"Wah? how rude, " Alice answered, feeling upset.

"Okay, okay, ruu-kun, you can tell her that later. okay" --> "Okay, okay, Ruu-kun. You can tell her that later. Okay.!?<one of them, last two can make up more persona.>" 

And with me ready and excited to try it, I take a deep breath, trying to clear my mind. --> took

ch4-Metal hammer: the same just for a hammer now.-

-Metal staff: finally, something new for a change. the same as the others, just that it could also be used as a metal club. Hmph.-

Hey, is it just me, or is the description weird? ----> This could easily be a thought. ---> 'Hey, is it just me, or is the description weird?'I've noticed a lack of proper guiding through distinction between dialogue, thoughts, and narration. Keep in mind that to give voice to the character, " character speaks." 'Character thinks.' Character pseudo-inner-voice aka narrator, mainly used to tell how/what oneself feels, sees, smells, tastes, etc.

ch 5: In a hospital hallway, a certain man was walking.  -> a certain man walked. (Using the right verb makes a readability difference.)