That's not it. (After all, had it been kept private merely for the matter of privacy, Ren wouldn't yap as much. If it were just a tiny piece of information, even if Ren finds it relevant, he wouldn't be this angry.

But it wasn't. It was a murderous thing, hellbent on hurting Ren and, from the state of Sumi when she arrived, everyone he holds dear. The possibilities of what could have happened were endless and Ren? Ren doesn't even know where to begin with how much went wrong due to Akechi's inability to let others in. Perhaps, had Ren known what haunts him from the beginning, this being would never have manifested in the first place.

A thousand thoughts roam through his head - he's pissed to the point he wants to leave, cool down and think this over, before the roles reverse and Ren's the one snapping... But he won't do any of the sort. Inhaling a deep breath, Ren lets the silence drag even though it's not on purpose; he's just attempting to structure his sentences, try to say what he means the best way possible.)

I understand you treasure your privacy. (And the words flow, accompanied by the deep, serious and thundering voice that usually replaces the calmness when he's this aggravated.) ... But this was above that. You should have told me, we could have defeated it together.