 If you liked
Under (xGround) Grand Hotel
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 ...then you might like
Deadlock
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Has a prison element and includes yaoi. However UGH is more graphic than Deadlock so go in prepared.
Both manga occur in prisons, but I'd say their similarities end there. Bc while Deadlock has gorgeous art, mature people and relationships (with no abuse whatsoever), UG is the opposite of it - it incorporates every element of yaoi that has given it a bad reputation, including abuse, rape and normalization of abusive behaviour as acceptable romantic gestures.