Chapter 351 ended the Ethan Stanley arc; he's off to India for retraining under his master, Cyril Rahman.
Chapter 352 will begin a new arc. I'm hoping that either it will have Tirawit Koukin's reappearance, so that we can learn his master's name; or that it will center around the Yami-YOMI master-disciple pair about which nothing significant has been revealed: not the style, not the master's identity nor the disciple's identity. IIRC, the only thing known about that pair is that their challenge-symbol is "Moon".
Another possibility is that we'll see the fruits of Ogata Isshinsai's training of the three shadowed figures shown
here in chapter 344. The central silhouette has been speculated to be the former Second Fist of Ragnarok, Berserker.
The YOMI run-down so far:
* Radin Tidat Jihan [Pencak Silat]. Presumed to have been killed by his own master for being a "failure".
* Kanou Shou [Karate]. Defeated by Kenichi. Died protecting Miu.
* Boris Ivanov [Command S.A.M.B.O]. Defeated by Kenichi. Disappeared after his master dismissed him. Presumably still searching for his imprisoned master.
* Tirawit Koukin [Muay Thai]. Defeated and "killed" Kenichi. Disappeared.
* Rachel Stanley [Lucha libre]. Defeated by Ma Renka. Master imprisoned. Now seemingly under Ryouzanpaku's protection.
* Kushinada Chikage [Jujutsu]. Relieved of task to kill Kenichi.
* Ethan Stanley [Kalarippayattu]. Defeated by Kenichi. Parted on good terms with Ken.
Remaining YOMI members:
- Three shadowed disciples of Ogata Isshinsai. One may be Berserker.
- Unknown user of unknown style with unknown master. Symbol, "Moon"
- Tirawit Koukin
- Kajima Satomi, YOMI leader, disciple of Fuurinji Saiga.