tentacle submission
When characters are not actively resisting tentacle_sex. Can potentially be willing participants, but generally suggests giving into the tentacle's lusts through physical or mental exhaustion or resignation. Can involve being bound or restrained, but tends to have either gone limp, or is actively attempting to encourage their attentions, though the submission is the most important part to this tag.
This can involve willing participants, so long as they are not dominating/controlling the tentacles.
Will rarely go alongside tentacle_rape, as submission suggests either partial willingness or loss of will, and the agression of rape will be lacking.