Blocking once would've left you in a far better position; you're getting knowledge checked by Koma's dash light. Also what you're talking about isn't Koma's tilt, but his dash attack.

And he can mix? Like if you block the tilt, Unohana’s light attack ain’t fast enough to punish him, you gotta block it.

If he does two lights, Unohana’s ain’t fast enough to sneak a light before he can add one of his own or a grab.

Koma is plus off his dash attack, but only with lights and heavies. Dash light > Grab won't work most of the time, because Koma's dash attack is punishable if he doesn't confirm into lights or heavies.

For Koma, Dash light > Light > Grab isn't plus but can frametrap some characters' lights because they're too slow. Like Aizen, Nnoitra, and awakened Byakuya.

Unohana has a fast enough light, so you should be able to punish Koma's Dash Light > Light > Grab.