Racing kings

The elderly woman rose and approached Mimoko as she finished setting up the board. 

Unlike with normal chess, each side controlled a vertical half and had no pawns. The starting area was the 1st and second ranks with the goal for the king to reach the 8th rank. Knights were placed on the e and d files, bishops on the f and c files, rooks on the g and b files, and the queens and kings on the h and a files with the kings at h2, and a2, respectively. The only other notable rule was that checks were not allowed, now could a king step on a square that would put it in check, adding another layer of strategy to the game.

"And you'll be the one playing, mother?" Ota asked as the elderly woman sat down.

"Yes, this concerns the family, so I, Benichiyo Inashiki, as head, must represent it. Now, I'm aware of those devices that can force chess games into law, however, none shall be used here. Thus, since lives are on the line, this will be considered an underground match in it's entirety."

Mimoko began by moving her king to h3 as Benichiyo moved her king to a3. "Hmm? Is she going to try and mirror me?" Mimoko thought as she moved her king to h4.

Sure enough, Benichiyo did and moved her king to a4. The again with king h5 and king a5, king h6 and king a6, but then after king h7, Benichiyo began to grin.

"Now I check you n' win-"

"And how will you do that?" Mimoko smirked.

Benichiyo scoured the board for and answer, but found none and let out a frustrated yell as she slammed her queen down on a5.

"Rookie mistake. Checkmate," Mimoko smiled as she moved her king to g8, winning the game.

"So be it. Get out. Your mother is disowned for good, and thus, you or any of your siblings are none of our concern."

"But moth-"

"OTA! You honor this!"

Ota scowled as Mimoko and Daria headed out. Once they had warped away, she turned to confront Benichiyo. 

"You threw on purpose."

"Cease your slander."

"Did you not agree-"

"Oma was the one who claimed Daria was trying to use our family name again. But regardless, the matter has been settled with this."

Ota refused to accept this, and secretly began plotting retaliation. "As the next head of the family, I won't allow my reign to be tainted from the onset by my failure of a sister and her offspring!" she angrily thought. 

...

Ichimitsu glanced up from his newspaper as Daria and Mimoko returned. "Was business settled?"

"Surprisingly well. It seems mother truly remained firm with her disownment of me," Daria sighed in relief.

"Then why were you so worried on the drive over?" Mimoko asked. 

A smirk formed on Daria's face. "Part of it was real, but I also figured it might goad you into suggesting racing kings."

"Why?"

"Well, mother likely felt that as head, she needed to take some form of action, so by goading you to challenge her to a chess variant, she could have an excuse to fall back on for letting the status quo stand."

"My mind can't quite process it. I think maybe I'll have an early dinner and go to bed."

...

The next day, Ota returned to Kawaguchi and shadowed Mimoko on her way to school. "I'll only honor Daria's disownment once her offspring are dealt with. She probably thinks she's got the edge in chess, but against me, my intellect will crush whatever skill she thinks she has," she thought as she reached for something in her pocket. 

"Are you heading for our school?" a voice asked from behind. 

Ota rolled her eyes as she turned to face Okisato. "Listen, boy, I have business, so don't interfere, lest you make an enemy of the Inashiki family."

"Of Tochigi? This isn't even your turf."

"It's a personal matter."

"With Inoue-senpai?"

Ota gritted her teeth. "Shall I teach YOU a lesson?"

Okisato shook his head and took off his coat and shirt. 

"How barbaric. I meant to engage intellectually- ...!?" 

Ota began to tremble as she laid eyes on the tattoo on Okisato's back. "K- Kana?" 

Okisato spun back around. "You know my mother!?" 

Ota's heart began to thump. "Y- Yes, we were good friend-"

"Liar."

Ota slowly began to retreat. 

"An old friend wouldn't act like she's seen a ghost just by the sight of my tattoo alone. Now if you played a role in killing her, that would make more logical sense."

"Cease the slander! It was just genuine shock. Don't accuse me of murder-"

Okisato pulled out a glowing DESPER key. "As soon as I got within a few feet of you, this began to glow. You know what that means, right? You have a DESPER AND you knew my mother. It's pretty easy to put two and two together. Seems it was the sinful seven, rather than the sinful six," he glared. 

The full game:

White: Mimoko Inoue (2870) Black: Tae Inashiki (1256)

1. Kh3 Ka3

2. Kh4 Ka4

3. Kh5 Ka5

4. Kh6 Ka6

5. Kg7 Qa5

6. Kg8#