Since Sacchin's BnBs are quite character-specific, I thought I'd experiment with all the characters and see what you can do after the 623B. All this is done in MBAC PC ver1.03b. Tests are based on this BnB:
2A 5B 2C 5C 623B (?) 623C 2C 5C airthrow
Use the list below to fill in the brackets with the command(s) based on the character you're facing.
All OTG 2Cs are 2 hits except for Shiki, Nanaya, VAkiha and probably other people I didn't notice. A OTG 2C will result in only 1 hit for some reason.
Midscreen
5B- All but Ciel, Miyako, Len, WLen (they just whiff through), Neco-Arc, NAC (you can't connect afterwards)
2B- Shiki, Arc, Ciel, Wara, Nanaya, Kouma, Sacchin, Nero
5C- Shiki, Arc, Ciel, Wara, Nanaya, Kouma, Sacchin, Nero
2C- Shiki, Ciel, Wara, Nanaya, Kouma, Miyako, Sacchin, Nero
5B2B- Shiki, Wara, Nanaya, Kouma, Sacchin, Nero
5B2C- Shiki, Wara, Nanaya, Kouma, Sacchin, Nero
2B5B, 2B5C, 2B2C, 5C5B, 5C2B, 5C2C, 2C5B, 2C2B, and 2C5C can't/shouldn't be used against anyone. The 623C can't connect after.
Corner (anywhere where the OTGed opponent's movement will be restricted by the corner)
5B- All but Ciel, Miyako, Len, WLen, Neco-Arc and NAC
2B- All but Miyako, Hisui, Len, WLen, Kohaku, MHisui and Necos
5C- All but Miyako, Hisui, Len, WLen, Kohaku, MHisui and Necos
2C- Aoko, Shiki, Arc, Ciel, Wara, Nanaya, Kouma, Miyako, Sacchin, Nero
5B2B- All but Ciel, Miyako, Len, WLen, Necos
5B2C- All but Ciel, Miyako, Len, WLen, Necos
2B2C- Aoko, Shiki, Ciel, Wara, Nanaya, Kouma, Miyako, Sacchin, Nero
5C2B- Wara alone
5C2C- Aoko, Shiki, Ciel, Wara, Nanaya, Kouma, Miyako, Sacchin, Nero
2C5B- All but Shiki, Nanaya, VAkiha, Necos
2C5C- Ciel, Wara, Kouma, Sacchin, Nero
5B5C, 2B5B, 2B5C, 5C5B and 2C2B should not be attempted.
My execution isn't top-notch so I may have slipped up a combo that could be possible on a character. I haven't attempted 3 attacks nor combos with 1 hit 2Cs. I'll update when I feel like it or when someone discovers something and tells me.
Notes
1)When fighting Necos, abandon all BnBs or switch character. You can't connect 623Cs after OTGs.
2)Len and WLen seem only to be hittable in corners using 2C5B. ONLY. Unless someone proves me wrong, which I hope.
3)IIRC, 5Cs do the most damage as OTGs.
Please test these out for yourselves and if I made any mistakes (which should be plenty) post in this thread.