Crouch on the lowest stair, then shinespark horizontally to bonk at the top corner of the grapple block. Down grab to get onto it.

Entrance condition:

"comeInShinecharged": {}

Requires:

{"shineChargeFrames": 110},
{"notable": "Shinespark Down-Grab to the Grapple Blocks (Left to Top)"},
"canSuitlessMaridia",
"h_underwaterCrouchJumpDownGrab",
"canHorizontalMidairShinespark",
{"shinespark": {"frames": 56, "excessFrames": 0}}

Dev note: This is only done suitless, as with Gravity, you can gravity jump up there. A similar strat can be done from the top right door, but it doesn't have a nice setup and has to be done midair. FIXME: Add a variant with canControlShinesparkEnd.