The groove, called “Hi” or “Bohi” in Japanese, has several purposes; it can make the blade lighter and more flexible or help draining the blood for instance, but some options are simply aesthetic (like Marudome). There are two kinds of options. One kind concerns the groove itself (standard, deep or no groove). These options are not available on lightweight blades. The other kind concerns the finish (Kakinagashi, 5 Bun Dome and Shinken hi). Of course, there are no finish available when the option is "without groove".
- Standard groove: the most classical groove.
- Deep groove: deeper groove than standard. It is useful to get a lighter blade and move the balance towards the Tsuka. It might also make the sound louder during cuts. Impossible to craft in the case of lightweight blades. The deep groove removes around 50 g from the blade's weight.
- Double groove (full custom Iaito only): consists in two shallow and thin grooves instead of one. The final weight of the blade is slightly superior to a standard groove (when combined with the finish options bellow, the cost of the finish is applied twice, once per groove). The standard finish for the bottom of the blade (Hi-dome) is Kakinagashi. "Standard Hi-dome" cannot be selected.
- Without groove: this option makes the blade heavier. Removing the groove increases the total weight by about 50 g on standard blades, and up to 150 g on heavy blades. The whistling sound disappears almost completely.
- Hi Dome: Standard: the groove has an ogival shape and stops approximately 4 cm from the Habaki.
- Hi Dome: Kakinagashi: the groove goes on under the Habaki. It makes the blade even lighter and moves the balance of the blade further towards the Tsuka.
- Hi Dome: 5 Bun Dome: the groove is moved closer to the Habaki (1.5 to 2 cm). It makes the blade slightly lighter and moves the balance of the blade towards the Tsuka.
- Hi Dome: Marudome: The groove is manually carved in a round shape on the Habaki end, similarly to most Shinken blades. This option is purely aesthetic.
- Hi Saki: Shinken: this kind of finish looks like the grooves that can be found on Shinken. The tips of the grooves where it connects with the Kissaki (tip of the blade) are manually and delicately crafted so that both merge very naturally in the form of a triangle (standard groove have an ogival shape). This option is particularly good-looking.