Stein doesn't consider the danger at all.
He's used to thinking of Spirit in his weapon form, solid and razor-edged, sowing death instead of reaping it. It takes a lot to injure a weapon proper and more to hurt a Death Weapon, and Stein hasn't seen Spirit really hurt during a fight since they were student partners together at the Academy. He thinks of the weapon as invincible, a constant he can always count on. Of course, he tends to forget that he's subject to mortality as well. Spirit never does, though. Stein doesn't have to remember when he has Spirit with him, to do that particular piece of remembering for him.
He doesn't think of the risk inherent in that.
In retrospect, it's a foolish assumption, sloppy thinking on his part born from the implicit trust he has in his weapon and how easy it is to let Spirit take over the considerations for morality and mortality while Stein himself gives himself over to the uncontrolled scream of Madness and combat.
The attacker in front of them is just going down; Stein knows they've won; the blood drying sticky on his skin and the languid satisfaction in his veins say so better than the dying light of the enemy's eyes. He steps forward even though it's unnecessary, reaching out to Soul Force the last shred of existence out of the shape in front of them. He can taste blood on his tongue and feel it clumping his hair into knots and he feels alive, with the crumpled forms of Kishin eggs around him and the weight of the scythe in his hand comforting in their familiarity.
His hand hits the form in front of him and sparks with electricity - and his other hand folds on itself, turning into a fist instead of a grip, and the surprise is almost but not quite enough to break off his Soul Force mid-spark. The jolt goes off, rocking him backward and shoving the enemy away, and Stein is turning before he has seen it hit, a protest forming on his lips.
As he turns his shoulder bumps against Spirit; the weapon is reaching out, moving in human form and Stein doesn't know why he's not in weapon form, is still trying to process what he's seeing when the attack - from behind him, he wasn't even paying attention to the danger - hits Spirit instead of Stein's unprotected back. There's a splash of color, like the weapon's hair is turning to liquid in the air, and then Spirit drops too fast for Stein to react. With the absence of the weapon there's just Stein staring blankly at the creature facing him. It's shaky on its legs - he must have mistakenly thought it was out for the count earlier in the fight - and for a breath there's just the empty-handed meister and the thing in front of him.
Stein's eyes focus on the red splashed across the attacker's claws, and some icy-cold voice in his head says, That's Spirit's blood, and he lifts his hand and lays it against the creature's chest. It rests there, linking the two of them into one shape, and then the meister's hand bursts with condensed soul wavelength and Stein watches the thing fly backward without blinking.
His knees hit the ground without his intention. It feels faintly like his legs have stopped working, or more precisely that his body has taken control of itself without checking in with the echoing silence in his head. He reaches out to touch Spirit's shoulder; the weapon is crumpled face-down on the ground, and when Stein's fingers brush the rumpled fabric of his coat the scythe doesn't stir or respond at all.
It's not terrifying. There's not anything in Stein's head at all but the quiet, like he's waiting for a response or a reaction or a movement from some outside source, any outside source. His knees are aching - he must have landed harder than he meant - and Spirit is very still against the ground. The scythe's arm is angled up over his head, like he tried to break his fall desperately, and Stein can't see his face, just the fall of red hair against the collar of his shirt and over his skin.
There is movement, then, just in the corner of his eye. Stein turns, very slowly, to face it. One of the fallen enemies is struggling to its feet, staring at him with the distant red glow of Kishin-egg-eyes. Stein doesn't move, just watches the thing move, and after a moment of hesitation as they gaze at each other it keeps going and pushes itself to its feet. When Stein doesn't react to that either, it steps forward. The movement is visibly tentative; the meister can see the tension in the thing's trembling form, like it's ready to run at a moment's notice.
He looks away as it steps forward, back at Spirit. There's still silence in his head. His thoughts stay quiet, even when his ears report the crunch of leaves under the approaching creature's feet. Even when claws tear through his shirt and shoulder alike, the bloom of hot pain isn't enough to make any sound in that silent pause.
Then the thing reaches for Spirit.
There's a screech, raw metal on metal inside the confines of Stein's skull, and an explosion of feeling, the reaction he's been waiting for. His hand is up and against flesh before he thinks, furious protectiveness flaring electric under his skin, and he's snarling "Don't touch him," as his soul wavelength shoves the threat back. It goes down, crumpling as bonelessly as Spirit has, and Stein's attention returns to the weapon's unmoving form. The dying gasps of the final attacker don't breach the wall of Stein's thoughts, and after a moment the panting rage of defensiveness goes silent again, and there's just Spirit still in front of him, and the cold of the air seeping into his bones, and the expectant quiet in his thoughts.