The Boktai games have many game mechanics that depend on the current date and time. The cartridges contain an RTC chip and a battery, which will keep track of the time even when the system is powered off. The games use the following values:

Date
Time
Sunrise/Sunset times in the player's selected region
Moon phase (based on current knowledge, only full moons are used currently. But the games track every moon phase, not just full moons)
Seasons

Region selection

When creating a save file (Boktai 1), or when starting the game with an uninitialized RTC (Boktai 2/3), the game will ask the player for their current location. This will affect the sunrise/sunset time calculation.

The list of regions is stored as a string in the game's script directory. Even though this is stored in the string list, the region list is stored as bytecode.

Example:

; Boktai 2 (U). String ID = 0x1b43
; Dumping from 0xce3dfb

i32 0x0 ; page number
	i32 0x1 ; number of regions in this page
		; region id
		i32 0x0
		; time zone offset (signed): 0x40 = +1 hour
		; When copying Japanese regions to an USA ROM, set this to -0x40 (c0 ff in hex editor)
		i32 0x0
		; longitude:
		;   in the eastern hemisphere: longitude_degrees * 2^16
		;   in the western hemisphere: (360 - longitude_degrees) * 2^16
		i32 0x0
		; latitude: latitude_degrees * 2^16
		i32 0x0
i32 0x1
	i32 0x1
		i32 0x1 ; St. John's
		i16 -0x320
		i32 0x13391ec
		i32 0x2f570a
i32 0x2
	i32 0x2
		i32 0x2 ; Labrador City
		i16 -0x340
		i32 0x1257333
		i32 0x3491ec
		i32 0x3 ; Halifax
		i16 -0x340
		i32 0x128a666 ; ≈ (360 - 63.59...) * 2^16
		i32 0x2c6148  ; ≈ 44.64... * 2^16
; etc...

i32 -0x1 ; done
i32 0x0
i32 0x0
i32 0x0
i32 0x0
i32 0x0
end

Japanese releases omit the time zone offset field (Japan only has a single time zone, JST). The region list is stored at these locations:

	Boktai 2 (U)	Boktai 2 (J)	Boktai 3
String ID	0x1b43	0x19bd	0x247c
Address	0x08ce3dfb	0x08d10af2	0x08dd3aa9

A map of all regions of Boktai 2 is available here: https://geojson.io/#id=gist:raphaelr/3b6f066014f8a5f6f84e9b50118c2c2c