use16
ORG 0x7C00

mov si, text_string
call print_string

jmp $

text_string db 'Launching KitsuneOS. Loading Kernel...Please Wait.',13,10,0

print_string:
        mov ah, 0x0E ; int 10h 'print char' function
_repeat:
        lodsb
        cmp al,0
        je loadkern     ; If char is zero, end of string
        int 10h                 ; Otherwise, print it
        jmp _repeat

loadkern: 
cld                ; Clear direction flag to ensure instructions like
                   ;    lodsb use forward movement.

xor ax, ax         ; AX=0 (use for segment)
mov ss, ax
mov sp, 0x7c00     ; Set up stack to grow down from 0x0000:0x07c00
                   ;    in region below the bootloader

mov es, ax         ; Read sector starting at 0x0000:0x7e00 (ES:BX)
mov bx, 0x7e00

mov ah, 2
mov al, 1
mov ch, 0
mov cl, 2
mov dh, 0
; mov dl, 0        ; Don't force to zero. Use value in DL passed by BIOS
                   ;     to our bootloader
int 13h

jmp 0x0000:0x7e00  ; Jump to physical address 0x07e00 by setting CS
                   ;     to 0 and IP to 0x7e00

times 510 - ($-$$) db 0
dw 0xAA55
    

use16
org 0x0000         ; Since CS will be 0x07e0 we need an origin of 0x0000
                   ;     0x07e0:0x0000 also represents phys addres 0x07e00
                   ;     0x07e0<<4 + 0x0000 = 0x7e00

; jmp main         ; Not necessary since main is next instruction

main:
mov ax, 0x07e0
mov ds, ax         ; Make sure segments are 0x07e0
mov es, ax

mov si, msg
call print
cli                ; Do CLI/HLT after we return from print
hlt                ;    Prevent code from getting beyond this point

print:
lodsb
cmp al, 0
je done
mov ah, 0eh
int 10h
jmp print
done:
ret

;Place data here. msg is a message we want to print
msg: db "Kernel Loaded. Welcome to Kitsune OS!"
    

fasm bootloader.asm boot.bin
fasm kernel.asm kernel.bin
dd if=boot.bin of=KitsuneOS.img bs=512 conv=notrunc
dd if=kernel.bin of=KitsuneOS.img bs=512 conv=notrunc seek=1
    

cld                ; Clear direction flag to ensure instructions like
                   ;    lodsb use forward movement.

xor ax, ax         ; AX=0 (use for segment)
mov ss, ax
mov sp, 0x7c00     ; Set up stack to grow down from 0x0000:0x07c00
                   ;    in region below the bootloader

mov es, ax
    

use16
org 0x0000         ; Since CS will be 0x07e0 we need an origin of 0x0000
    

jmp 0x0000:0x7e00  ; Jump to physical address 0x07e00 by setting CS
                   ;     to 0 and IP to 0x7e00
    

Bootloader and "Kernel" or Stage 2 don't really know if I must use a second boot file really,

Just curious - what hardware you have???
If you are cd/dvd owner - you can burn cd in floppy emulation mode.. Many software tools have this option (for sure ex. CD burner XP WIndows tool).

...
The above instructions really belong to directly below the 'ORG 0x7C00' directive. Also the 'mov ds, ax' instruction is still missing, and the print_string procedure relies on it being set up properly!

Do notice that the first comment in KERNEL.ASM

Code:

use16
org 0x0000         ; Since CS will be 0x07e0 we need an origin of 0x0000
    

does not match the far jump in the BOOTLOADER.ASM

Code:

jmp 0x0000:0x7e00  ; Jump to physical address 0x07e00 by setting CS
                   ;     to 0 and IP to 0x7e00
    

Quote:

Bootloader and "Kernel" or Stage 2 don't really know if I must use a second boot file really,

The bootloader code must fit in only 512 bytes. If your kernel is to be any serious, then it won't be possible to stay within those 512 bytes. So yes, you need 2 files.

This source code works despite what you said about the jump to adress command
I have tested it.