I pulled the game up on Youtube and I see it uses kanji, which will make dumping the text a lot more difficult since you'll have to identify every single kanji. I just opened the ROM in Tile Molester, displayed the data in 1bpp planar, and found the character set at $18100. I counted 1247 kanji - yes, over a thousand. So any text dump will require identifying all of those, and I don't know how the text is stored either. It's a 4MB ROM, which is huge for the Game Boy, so if you're lucky it won't be compressed.
Just out of curiosity, I did a relative search for four characters on the intro screen and found the text in the ROM (starting $106091), and I see how it is done: normal characters just take a normal byte, while kanji takes the number of the 'page' (whatever) and then the kanji on that page. So Sakura Taisen is "B6 B0 EB 04 0E 03 A8", if that makes sense.
I had a go at a simple table (in Romaji) but there are a lot of kanji that need to be done here. Still, gives you a starting point.
10=
11=0
12=1
13=2
14=3
15=4
16=5
17=6
18=7
19=8
1A=9
1B=A
1C=B
1D=C
1E=D
1F=E
20=F
21=G
22=H
23=I
24=J
25=K
26=L
27=M
28=N
29=O
2A=P
2B=Q
2C=R
2D=S
2E=T
2F=U
30=V
31=W
32=X
33=Y
34=Z
35=a
36=b
37=c
38=d
39=e
3A=f
3B=g
3C=h
3D=i
3E=j
3F=k
40=l
41=m
42=n
43=o
44=p
45=q
46=r
47=s
48=t
49=u
4A=v
4B=w
4C=x
4D=y
4E=z
4F=xa
50=a
51=xi
52=i
53=xu
54=u
55=xe
56=e
57=xo
58=o
59=ka
5A=ga
5B=ki
5C=gi
5D=ku
5E=gu
5F=ke
60=ge
61=ko
62=go
63=sa
64=za
65=shi
66=ji
67=su
68=zu
69=se
6A=ze
6B=so
6C=zo
6D=ta
6E=da
6F=chi
70=dji
71=tt
72=tsu
73=du
74=te
75=de
76=to
77=do
78=na
79=ni
7A=nu
7B=ne
7C=no
7D=ha
7E=ba
7F=pa
80=hi
81=bi
82=pi
83=fu
84=bu
85=pu
86=he
87=be
88=pe
89=ho
8A=bo
8B=po
8C=ma
8D=mi
8E=mu
8F=me
90=mo
91=xya
92=ya
93=xyu
94=yu
95=xyo
96=yo
97=ra
98=ri
99=ru
9A=re
9B=ro
9C=xwa
9D=wa
9E=,
9F=.
A0=wo
A1=nn
A2=XA
A3=A
A4=XI
A5=I
A6=XU
A7=U
A8=XE
A9=E
AA=XO
AB=O
AC=KA
AD=GA
AE=KI
AF=GI
B0=KU
B1=GU
B2=KE
B3=GE
B4=KO
B5=GO
B6=SA
B7=ZA
B8=SHI
B9=JI
BA=SU
BB=ZU
BC=SE
BD=ZE
BE=SO
BF=ZO
C0=TA
C1=DA
C2=CHI
C3=DJI
C4=TT
C5=TSU
C6=DU
C7=TE
C8=DE
C9=TO
CA=DO
CB=NA
CC=NI
CD=NU
CE=NE
CF=NO
D0=HA
D1=BA
D2=PA
D3=HI
D4=BI
D5=PI
D6=FU
D7=BU
D8=PU
D9=HE
DA=BE
DB=PE
DC=HO
DD=BO
DE=PO
DF=MA
E0=MI
E1=,,
E2=MU
E3=ME
E4=MO
E5=XYA
E6=YA
E7=XYU
E8=YU
E9=XYO
EA=YO
EB=RA
EC=RI
ED=RU
EE=RE
EF=RO
F0=XWA
F1=WA
F2=[dot]
F3=[center]
F4=WO
F5=NN
F6=VU
F7=XKA
F8=XKE
F9=?
FA=!
FB=-
FC=~
FD=[open]
FE=[close]
FF=[..]
This might have errors and I think everything under $10 is a control code (next line, choose kanji page etc) so someone will have to check that out.
I won't be doing this myself, but at least someone else knows where to begin. Good luck!
